Why did Joas turn from temple repair to killing Zacharias?

Joas was seven years old when he began to reign, and he reigned for forty years in Jerusalem, born of his mother Sebia of Bersabee. Throughout the lifetime of High Priest Joiada, Joas did that which was right in the sight of the Lord. Under Joiada's direction, two wives were chosen for the king, by whom he fathered sons and daughters. During this period, Joas resolved to repair the house of the Lord, which had been ransacked and damaged by the wicked Athalia and her sons, who had taken consecrated temple furnishings to decorate the temple of Baal.

Joas first ordered the priests and Levites to collect money yearly from the cities of Juda for temple repairs and to act quickly. When the Levites were negligent, he challenged Joiada about their failure to bring the money appointed by Moses from Juda and Jerusalem. Joas then instituted a public collection. At the king's command, a chest was made and set outside by the gate of the house of the Lord. A proclamation was sent throughout Juda and Jerusalem urging every citizen to bring the tax that Moses, the servant of God, had appointed for Israel in the wilderness. The leaders and all the people rejoiced, bringing their contributions and casting them into the chest until it was filled. When it was time to bring the chest before the royal officers by the hands of the Levites, the king's scribe and he whom the high priest had appointed went in, poured out the accumulated money, and carried the chest back to its place. This procedure was carried out daily, amassing an abundant sum. The king and Joiada gave the money to the work overseers, who hired stonecutters, other craftsmen, and workers in iron and brass to restore the house of the Lord and support what was falling. The workers closed the breaches, restored the house to its former state, and made it firm. When the work was finished, they returned the surplus to the king and Joiada. With the remaining funds, sacred gold and silver vessels were crafted for the service and holocausts, which were offered continually in the house of the Lord all the days of Joiada.

Joiada grew old and full of days, dying at the age of one hundred and thirty years, and was buried in the city of David among the kings because he had done good to Israel and to God's house. Following Joiada's death, the princes of Juda went in and bowed before King Joas; the king was soothed by their services and hearkened to them. The royal court abandoned the temple of the Lord God of their fathers, turning to serve pagan groves and idols, which brought divine wrath upon Juda and Jerusalem. Although God sent prophets to testify against them and turn them back, the people refused to listen. When the Spirit of God clothed Zacharias, the son of Joiada the priest, he stood in the sight of the people and warned that their transgression would not be for their good: because they had forsaken the Lord, He would forsake them. Conspiring against him, the leaders stoned Zacharias at the king's commandment in the court of the house of the Lord. Joas remembered not the kindness that Joiada had shown him, but slew his son, whose dying prayer called upon the Lord to see and require it.

When a year was come about, the army of Syria marched up against Joas, invaded Juda and Jerusalem, killed all the princes of the people, and sent all the spoil to the king of Damascus. Although the Syrian army arrived with a very small number of men, the Lord delivered into their hands an infinite multitude because Juda had forsaken the Lord the God of their fathers, and the Syrians executed divine judgments on Joas. When the invaders departed, leaving the king afflicted with great diseases, his own servants conspired against him for the blood of the son of Joiada the priest, assassinating Joas in his bed. The conspirators were Zabad the son of Semmaath an Ammonitess, and Jozabad the son of Semarith a Moabitess. Joas was buried in the city of David, but was denied a place in the sepulchres of the kings, The chapter refers the account of his sons, the money gathered, and the temple repairs to the book of kings. His son Amasias succeeded him.