The princes of Judah - made obeisance to the king - I believe the Targum has given the true sense of this verse: "After the death of Jehoiada, the great men of Judah came and adored King Joash, and seduced him; and then the king received from them their idols."
The nobles had taken part in the revolution which placed Joash on the throne 2 Chronicles 23:2, 2 Chronicles 23:13, 2 Chronicles 23:20, but probably on political rather than on religious grounds. They might dislike the rule of a woman and a foreigner without participating in the zeal of Jehoiada for purity of religion. They now petitioned for a toleration of idolatry, not for a return to the condition of things which prevailed under Athaliah. No doubt they carried a considerable party with them; but the temple-worship continued, as appears from the history of Zechariah 2 Chronicles 24:20. Nor is the king taxed personally with idolatry.