The relationship between Joash (also called Jehoash) and the priesthood, was an especially complicated one. I suggest that the priests lost trust in him because he had begun to adopt some of Athaliah's policies. Moreover, based on 2 Chron. 24:7, they probably blamed him for failing to protect the Temple and held him responsible for costly items stolen from the Temple by his relatives. They made the repairs only when Joash provided enough money to replace the Temple furnishings, in addition to making the repairs.
Joash, although he was a royal son, had been raised by in the Temple after having been benevolently kidnapped by his aunt and the high priest Jehoiada at the beginning of the reign of Joash's grandmother, Queen Athaliah. After six years, Jehoiada mustered his military allies and declared the seven-year-old Joash to be the rightful ruler, also orchestrating the murder of the child's grandmother (2 Kings 11). Joash followed Jehoiada's lead during the remaining years of his childhood but established independence as an adolescent or adult. One way he did so was by tolerating unauthorized worship, which no doubt strained the relationship with the priests of Yahweh. He also seems to have turned a blind eye to a robbery of the Temple by a faction associated with his Athaliah (see below).
Joash did that which was right in the sight of the Lord all his days
wherein Jehoiada the priest instructed him. But the high places were
not taken away; the people still sacrificed and burned incense in the
high places. (2 Kings 12)
We are not told exactly when Joash ordered the repairs to be made, but it we can speculate with good reason that his support of sacrifices at the high places caused the priests serious concern. 2 Chronicles 24:7 adds that:
The [other] children of Athaliah, that wicked woman, had broken into
the house of God and had even used all the dedicated things of the
house of the Lord for the Baals.
I suggest that the placement of this verse, immediately after Joash's questioning of the priests, implies that the break-in was the reason why the repairs had not been made. It was certainly a major blow the Temple. The priests would have felt that Joash failed in his duty to protect the Temple. No doubt they also needed money to replace the holy vessels and silver and golden ornaments that had be stolen. Indeed, it is immediately after Joash provided the funds that the repairs were made and the costly ornaments were replaced.
So the king gave command, and they made a chest and set it outside the
gate of the house of the Lord... So those who were
engaged in the work labored, and the repairing went forward at their
hands, and they restored the house of God to its proper condition and
strengthened it. When they had finished, they brought the rest of
the silver to the king and Jehoiada, and with it were made utensils
for the house of the Lord, utensils for the service and for the burnt
offerings, and ladles, and vessels of gold and silver. They offered
burnt offerings in the house of the Lord regularly all the days of
The Bible does not report the conversation but I suggest that the priests told the king they would repair the Temple if and when he provided the funds not only for the repairs but for the replacement of the costly ornaments his relatives stole and dedicated to Baal.
This scenario is necessarily speculative, but it is clear that tensions between priesthood and the king form the background of this drama. These tensions resulted from the complicated relationship between Joash and the high priest who raised him but also brought about his grandmother Athaliah's death. The stress reach a climax by the theft of Temple furnishing by Joash's relatives.
Note: commentators are divided as to whether the "children [lit. sons] of Athaliah" refers to her own sons or to people devoted to her legacy.