Therefore King Jehoash summoned Jehoiada the priest and the other priests and said to them, “Why are you not repairing the house? Now therefore take no more money from your donors, but hand it over for the repair of the house.”
2 Kings 12:7

God didn't choose the sons of Aaron as his priests because they were more scrupulous or more righteous than others. They were just as prone to fraud and wasteful behavior as anyone else. Apparently they much preferred spending donations on flashy baubles--and probably on personal gain--than on much needed repairs to the Temple.

Jehoash's solution was a system of checks and balances: accounting by representatives of two branches of the government and at least two witnesses to every transaction.