Why were the kings after Solomon bad kings?

Answer 1

It is important to understand that the Book of Kings was written in the Kingdom of Judah during the seventh-century-BCE reign of King Josiah. They were written for a Judahite audience, not so much for an Israelite one, they were intended to foster national pride, but also national unity among the descendants of the refugees from the former kingdom of Israel and perhaps to justify a Judahite claim on the 'lost' territory of Israel, now Samaria.

Arguably, the stories of Saul, David and Solomon were romantic tales intended to create a glorious past that the Judahites could be proud of. The depiction of a united monarchy, disputed by some important scholars, provided comfort for the former Israelite refugees now living in Judah and a reason to hold Israel as a lost territory to be reconquered.

Some national rivalry creeps in, as the Book of Kings consistently depicts the kings of Israel as worse than those of Judah, but even the kings of Judah generally get a bad press. It has been suggested that if there was a minority sect that held the "Yahweh-only" views written in the Book of Kings and more generally in the Deuteronomic History as a whole, then that sect must have been at constant loggerheads with the kings of Judah. Those few Judahite kings who received a more favourable mention in Kings before the time of Josiah, are depicted as favouring the worship of Yahweh (God) before all other gods. This includes Hezekia, who is said in The Bible to have attempted unsuccessfully to introduce monotheism.

A different answer: not all of the kings after Solomon were bad. Some of them were very righteous, as stated in the book of Kings. Those who were not righteous were lax in various Torah-laws, such as the prohibition against idolatry.