John Gill Commentary 2 Kings 23:32

"And he did that which was evil in the sight of Jehovah, according to all that his fathers had done." — 2 Kings 23:32 (ASV)

And he did that which was evil in the sight of the Lord
Committed idolatry:

according to all that his fathers had done
his grandfather and great-grandfather, Amon and Manasseh; so soon after Josiah's death was the revolt to idolatry.