As the king goes, so goes the country. Hezekiah was a man who lived for the flesh with no concern over the future... and so was his kingdom.
08085 שׁמע shama‘ , hear, hearken, obey,...
13 And Hezekiah hearkened <08085> unto them, and shewed them all the
house of his precious things, the silver, and the gold, and the
spices, and the precious ointment, and all the house of his armour,
and all that was found in his treasures: there was nothing in his
house, nor in all his dominion, that Hezekiah shewed them not.
16 And Isaiah said unto Hezekiah, Hear <08085>the word of the LORD.
I have noted the Strong's numbers above to demonstrate that Isaiah had changed his normal introduction of "Thus sayeth the Lord" to "Hear". Isaiah is telling us that Hezekiah had not only heard but obeyed men rather than God. This subtle change tells us that it was wrong for Hezekiah to listen to men rather than God, and the showing of the possessions was simply the outcome of his deeper disobedience.
Hezekiah's response to God's punishment is instructive of his heart attitude:
19 Then said Hezekiah unto Isaiah, Good is the word of the LORD which
thou hast spoken. And he said, Is it not good, if peace and truth be
in my days?
God had spelled out horrible long term consequences, but Hezekiah thinks it is a good word since things will be OK in his day. Hezekiah is not listed in the rolls of the faithful because it cannot be said of him:
Heb 11:13 These all died in faith, not having received the promises,
but having seen them afar off, and were persuaded of them, and
embraced them, and confessed that they were strangers and pilgrims on
the earth. 14 For they that say such things declare plainly that they
seek a country.
Hezekiah was blind to the future and lived for the moment.
God had warned many years ago that they should hearken unto him:
Le 26:14 But if ye will not hearken unto me, and will not do all
these commandments; Le 26:18 And if ye will not yet for all this
hearken unto me, then I will punish you seven times more for your
sins. Le 26:21 And if ye walk contrary unto me, and will not hearken
unto me; I will bring seven times more plagues upon you according to
your sins. Le 26:27 And if ye will not for all this hearken unto me,
but walk contrary unto me;
So Hezekiah was without excuse though he was merely the federal representative of the people. They were in the same heart condition.