Albert Barnes Commentary 2 Kings 21:17

"Now the rest of the acts of Manasseh, and all that he did, and his sin that he sinned, are they not written in the book of the chronicles of the kings of Judah?" — 2 Kings 21:17 (ASV)

The writer of Kings recounts the history of fifty-five years in just eighteen verses and, as a result, omits numerous important facts from Manasseh's life. Among the most remarkable facts omitted are Manasseh's capture by the king of Assyria, his removal to Babylon, his repentance there, his restoration to his kingdom, and his religious reforms upon his return. These events are recorded only in Chronicles (see the marginal reference and note).

The writer of Kings likely omitted these events because he viewed Manasseh's repentance as merely a half-repentance, followed by a half-reformation that left the root of the evil untouched.