A note on this revision: (see also Comments on revision:) -- In the process of reshaping
this into a better answer; the OP's "What could have been the compelling reason for this?" eventually overpowered, any sense of satisfaction, I could find, in my original answer; more so, the further I looked.
The "...compelling reason for this.."; I now find, throughout this whole epicenter, of divisions and fulfillment. I find nothing casual about this, from (1 Kings 19:1) to (2Ki 9:37). I still hold to my answer, and for the same reasons, which I came back to clarify; there is nothing in the text that suggests that God changed his mind. On the contrary, it is God's mind; the foresight, and ordering of these events; that has turned this answer, back on myself; now, an endless source, of questions.
Why (1 Kings 19:1) to (2 Kings 9:37)?
Some relevant events, leading up to the OP reference: 1 Kings 19:15-16
-- I grant, that there is an obvious disparity, between the commandment, and the indirection to its fulfillment. There is also, no shortage of it, in regard to the observation. Being that the question is central, to Elijah and Jehu; to mark, the beginnings and endings, of any association; especially one, involving the direct fulfillment, of an immediate prophecy; seems prudent. In this case, I am referring to a conclusion, of an epic.
(1 K1 18:4) both abridges, and incites expectation; regarding this brazen act of rebellion, and God's answer to it; the end of what begins here, to rage, between these two peaks of event. "...when Jezebel cut off the prophets of the LORD", there.
Elijah responds in kind, here (1 Ki 19:2). "Elijah said unto them, Take the prophets of Baal; let not one of them escape...Elijah brought them down to the brook Kishon, and slew them there."
When "...Ahab told Jezebel all that Elijah had done (1 Ki 19:2)." Jezebel responds with an oath against Elijah's life.
(1Ki 19:2) Then Jezebel sent a messenger unto Elijah, saying, So let the gods do to me, and more also, if I make not thy life as the life of one of them by to morrow about this time."
This sets in motion, the course of events, that lead directly to the OP's reference of (1 Kings 19:15-18); ultimately proving to be God's judgment, of the whole matter, as I intend to show. In this context, all associations must be confined, to the common link between Elijah, Ahab, Jezebel, and Jehu; though the broader implications are far reaching, with respect to God's judgment, against Israel's idolatry. This, can be viewed, with consideration of God's command to anoint Hazael, as king of Syria; causing Elisha to weep. (2Ki 8:12) And Hazael said, Why weepeth my lord? And he answered, Because I know the evil that thou wilt do unto the children of Israel..." Please consider this as an aside, as I leave no dependency on those implications. It is noteworthy.
This developmental, introduction, is longer than I would like. However, I felt obligated to provide justification; for what some might perceive, as taking unnecessary liberty, with the scope of the OP's question. I feel that there is an imperative relevancy, that must be considered, when trying to answer this question.
Proceeding from the threat, to the refining conclusion, of God's judgement
Elijah flees, to Beersheba, for his life (v.3). Leaving his servant there, he travels a days journey into the wilderness; coming to a juniper tree, he asks God to let him die (v.4), and falls asleep (v.5). Twice hereafter, he is awakened by the angel of the LORD.
(1Ki 19:7) And the angel of the LORD came again the second time, and touched him, and said, Arise and eat; because the journey is too great for thee.
Then this happens.
(1Ki 19:8) And he arose, and did eat and drink, and went in the strength of that meat forty days and forty nights unto Horeb the mount of God.
Followed by this.
(1Ki 19:11) And he said, Go forth, and stand upon the mount before the LORD. And, behold, the LORD passed by, and a great and strong wind rent the mountains, and brake in pieces the rocks before the LORD; but the LORD was not in the wind: and after the wind an earthquake; but the LORD was not in the earthquake:
Much like this.
(Exo 33:22) And it shall come to pass, while my glory passeth by, that I will put thee in a cleft of the rock, and will cover thee with my hand while I pass by:
Beyond noticing; a hundred times before, this never developed into consideration.
"The history of Israel has never touched Horeb since Moses left it, and it is not without significance that we are once more on that sacred ground. The parallel between Moses and Elijah is very real (MacLaren, Alexander.
Expositions of Holy Scripture. Pub.(1904-1910), public domain)."
see 1 Ki 19:1-18. This commentary.
"...however the nutritive virtue of it, by which he was supported, and held out till he came to Horeb or Sinai; called the mount of the Lord, because here he had appeared to Moses in the bush, and from hence gave the law to the children of Israel. Abarbinel is of opinion that this term of forty days was consumed in his whole journey to Horeb, his stay there, and return to the land of Israel (Gill,John, D.D., (1697-1771)
Pub. (1746-1766), 1816; public domain)." See 1 Ki 19:8, this commentary.
Immediately after the previous events, and being in the same place; the OP's first references are found.
(1Ki 19:15) And the LORD said unto him, Go, return on thy way to the wilderness of Damascus: and when thou comest, anoint Hazael to be king over Syria:
(1Ki 19:16) And Jehu the son of Nimshi shalt thou anoint to be king over Israel: and Elisha the son of Shaphat of Abelmeholah shalt thou anoint to be prophet in thy room.
Elijah proceeds directly, to find Elisha
God directed his commandment to the office (see Comments on revision:)*, which at the time was occupied by Elijah; who upon receiving the commandment, directly proceeds to find Elisha.
(1Ki 19:19) So he departed thence, and found Elisha the son of Shaphat, who was plowing with twelve yoke of oxen before him, and he with the twelfth: and Elijah passed by him, and cast his mantle upon him.
Without record of any exchange between them, Elijah confers his mantle upon Elisha. "Beyond this is a sea of speculation about the order of office up until the point where Elijah is taken up (2 Ki 2:11 see Comments on revision: Beyond this.".
Elijah returns to Ahab, God pronounces judgments
(1Ki 21:17) And the word of the LORD came to Elijah the Tishbite, saying,
(1Ki 21:18) Arise, go down to meet Ahab king of Israel, which is in Samaria: behold, he is in the vineyard of Naboth, whither he is gone down to possess it.
(1Ki 21:19) And thou shalt speak unto him, saying, Thus saith the LORD, Hast thou killed, and also taken possession? And thou shalt speak unto him, saying, Thus saith the LORD, In the place where dogs licked the blood of Naboth shall dogs lick thy blood, even thine.
(1Ki 21:20) And Ahab said to Elijah, Hast thou found me, O mine enemy? And he answered, I have found thee: because thou hast sold thyself to work evil in the sight of the LORD.
(1Ki 21:21) Behold, I will bring evil upon thee, and will take away thy posterity, and will cut off from Ahab him that pisseth against the wall, and him that is shut up and left in Israel,
(1Ki 21:22) And will make thine house like the house of Jeroboam the son of Nebat, and like the house of Baasha the son of Ahijah, for the provocation wherewith thou hast provoked me to anger, and made Israel to sin.
Ahab spares his own life, by repenting at the judgment (1 Ki 21:25-29).
(1Ki 21:29) Seest thou how Ahab humbleth himself before me? because he humbleth himself before me, I will not bring the evil in his days: but in his son's days will I bring the evil upon his house.
(1 Ki 21:23) And of Jezebel also spake the LORD, saying, The dogs shall eat Jezebel by the wall of Jezreel.
Shortly after this, Elijah is taken up. Ultimately, God's judgment upon Ahab, and Jezebel is carried out, by none other than Jehu himself (2 Ki 9:30-36 following).
(2Ki 2:11) And it came to pass, as they still went on, and talked, that, behold, there appeared a chariot of fire, and horses of fire, and parted them both asunder; and Elijah went up by a whirlwind into heaven.
(2Ki 2:12) And Elisha saw it, and he cried, My father, my father, the chariot of Israel, and the horsemen thereof. And he saw him no more: and he took hold of his own clothes, and rent them in two pieces.
(2Ki 2:13) He took up also the mantle of Elijah that fell from him, and went back, and stood by the bank of Jordan;
(2Ki 2:14) And he took the mantle of Elijah that fell from him, and smote the waters, and said, Where is the LORD God of Elijah? and when he also had smitten the waters, they parted hither and thither: and Elisha went over.
It might be noteworthy to mention Elisha's obvious connection to the mantle of Elijah in the inaugural phase of this transition (2 Kings 2:13), which is not a trivial thing considering that it was his warrant to the office.(1Ki 19:19) Also, Elisha's passing over the Jordan, in this manner, is not insignificant; nor is this precise location, being reminiscent of a past, critical event; the end of 40 years; Israel's wandering. Israel crossed over in the same manner; the end of an exodus. Israel's first, intentional, encounter was Jericho.
After its destruction --
And Joshua adjured them at that time, saying, Cursed be the man before the LORD, that riseth up and buildeth this city Jericho: he shall lay the foundation thereof in his firstborn, and in his youngest son shall he set up the gates of it.
This is also significant. 'And in his days', refers to Ahab, from vs.29-34(below), which is a synopses of his reign; the last being the following verse. The building of Jericho, is the last indictment of the litany, this is entailed on the judgement which is about to follow.
(1 Kings 16:34) And in his days did Hiel the Bethelite build Jericho,.... Which was forbidden by Joshua under an anathema; but this man, either ignorant of that adjuration of Joshua, or in contempt and defiance of it, and knowing it might please the king and queen, set about the rebuilding of it; and it being done by the leave and under the authority of Ahab, is mentioned together with his wicked actions:
he laid the foundation thereof in Abiram his firstborn: that is, his firstborn died as soon as he laid the foundation of the city, but this did not deter him from going on with it:
and set up the gates thereof in his youngest son Segub; all the rest of his children died as he was rebuilding the city, until only his youngest son was left, and he was taken off by death just as he had finished it, signified by setting up the gates of it: all which was
according to the word of the Lord, which he spake by Joshua the son of Nun: between four hundred and five hundred years ago. It was after this a place of great note, and so continued many hundreds of years (Gill, John, D.D., (1697-1771). Pub. 1746-1766, 1816; public domain)." see (1 Kings 16:34) this commentary.
This is the very place, where Elijah was taken up, and Elisha became the agent, of God's Word to Israel.
2 Kings 2:4
And Elijah said unto him, Elisha, tarry here, I pray thee; for the LORD hath sent me to Jericho. And he said, As the LORD liveth, and as thy soul liveth, I will not leave thee. So they came to Jericho.
Elijah has been taken up. Further course of events; set in motion by Elisha
(2 Ki 8:12-15) is the account of Hazael's ascension to the throne of Syria, by treacherously murdering his king, Benhadad, at Damascus. There is no account of Elisha anointing, but only prophesying, to Hazael; and weeping for cruelties, which Hazael will perpetrate upon God's people.
Jehu the son of Jehoshephat, son of Nimshi, was indeed anointed king over Israel as God commanded. Onerous speculation on the point of his relationship to Nimshi as Grandfather, I refuse to engage, as I believe most would. Take note here of this second level of indirection to the commandment (2 Kings 9:1). Elisha delegates one of the children of the prophets to execute the commandment, which he goes about precisely as Elisha foresees.
(2Ki 9:1) And Elisha the prophet called one of the children of the prophets, and said unto him, Gird up thy loins, and take this box of oil in thine hand, and go to Ramothgilead:
(2Ki 9:2) And when thou comest thither, look out there Jehu the son of Jehoshaphat the son of Nimshi, and go in, and make him arise up from among his brethren, and carry him to an inner chamber;
(2Ki 9:3) Then take the box of oil, and pour it on his head, and say, Thus saith the LORD, I have anointed thee king over Israel. Then open the door, and flee, and tarry not.
(2Ki 9:4) So the young man, even the young man the prophet, went to Ramothgilead.
(2Ki 9:5) And when he came, behold, the captains of the host were sitting; and he said, I have an errand to thee, O captain. And Jehu said, Unto which of all us? And he said, To thee, O captain.
(2Ki 9:6) And he arose, and went into the house; and he poured the oil on his head, and said unto him, Thus saith the LORD God of Israel, I have anointed thee king over the people of the LORD, even over Israel.
Jehu executes the judgement, pronounced on Jezebel, by God, through Elijah
(2Ki 9:30) And when Jehu was come to Jezreel, Jezebel heard of it; and she painted her face, and tired her head, and looked out at a window.
(2Ki 9:31) And as Jehu entered in at the gate, she said, Had Zimri peace, who slew his master?
(2Ki 9:32) And he lifted up his face to the window, and said, Who is on my side? who? And there looked out to him two or three eunuchs.
(2Ki 9:33) And he said, Throw her down. So they threw her down: and some of her blood was sprinkled on the wall, and on the horses: and he trode her under foot.
(2Ki 9:36) Wherefore they came again, and told him. And he said, This is the word of the LORD, which he spake by his servant Elijah the Tishbite, saying, In the portion of Jezreel shall dogs eat the flesh of Jezebel:
Jehu executes God's judgement on the house of Ahab, by the word of Elijah
(2Ki 10:10) Know now that there shall fall unto the earth nothing of the word of the LORD, which the LORD spake concerning the house of Ahab: for the LORD hath done that which he spake by his servant Elijah.
(2Ki 10:11) So Jehu slew all that remained of the house of Ahab in Jezreel, and all his great men, and his kinsfolks, and his priests, until he left him none remaining.
This is the complete, and direct, fulfillment, of all of God's Judgements, pronounced by the word of Elijah; concerning, Ahab and Jezebel; and the rise of idolatry, in Israel, that issued from their union; the true origin, of this epic.
(1Ki 16:30) And Ahab the son of Omri did evil in the sight of the LORD above all that were before him.
(1Ki 16:31) And it came to pass, as if it had been a light thing for him to walk in the sins of Jeroboam the son of Nebat, that he took to wife Jezebel the daughter of Ethbaal king of the Zidonians, and went and served Baal, and worshipped him.
(1Ki 16:32) And he reared up an altar for Baal in the house of Baal, which he had built in Samaria.
(1Ki 16:33) And Ahab made a grove; and Ahab did more to provoke the LORD God of Israel to anger than all the kings of Israel that were before him.
(1Ki 16:34) In his days did Hiel the Bethelite build Jericho: he laid the foundation thereof in Abiram his firstborn, and set up the gates thereof in his youngest son Segub, according to the word of the LORD, which he spake by Joshua the son of Nun.
"From the beginning of his reign Ahab set aside both the First and the Second Commandment. His marriage with Jezebel, the young and beautiful Sidonian princess, plunged him and his kingdom into yet deeper darkness. In addition to Jeroboam’s calves, the worship of Baal, the sun-god, was shamelessly introduced, and his temple was served by hundreds of priests. The inspired artist does not hesitate to paint with Rembrandt colors, and the illustrious glory of Elijah shows clearly against the dark background. The darkest hour precedes the dawn; the keenest pain ushers in birth. First Ahab and Jezebel, then Elijah (F. B. Meyer, B.A. A Devotional Commentary. Pub. 1914; public domain. see 1 Kings 16:29-17:7 this commentary)."
While, there is no textual instigation, that supports the idea that God changed his mind; I don't see that there is, and my claim is that he did not.; this is nothing so simple, as a 'Play by Play'; and there is plenty of instigation provoking this question: "What could have been the compelling reason...". If this is the OP's real question; I suspect, answers beyond this, reside somewhere in that "...sea of speculation...", that I boarded up in my first post. I would also like to know.
Comments on revision:
Initially, I intended only to expand, two narrow statements.
"God directed his commandment to the office..." All of these judgements, and appointments, are attributed to God, throughout the text; the way that they are brought about, seems to suggest that God is directing, more-so, than he is delegating. Regardless, I see no breaches, or impediments, to his will, in the text.
and especially this one.
"Beyond this is a sea of speculation..."
This is a chasm; the obligation is to build a bridge, not board it up; worse, leave no markings at all.
This whole account is full, of persistent shadows.