The worship on the “high places” seems to have continued uninterruptedly to the time of Hezekiah, who abolished it 2 Kings 18:4. It was, however, again established by Manasseh, his son 2 Kings 21:3. The priests at this time cannot have regarded it as idolatrous, or Jehoiada would have put it during his regency.
Related Commentaries of 2 Kings 12:3
2 Kings 12:3
3 But the high places were not taken away: the people still sacrificed and burnt incense in the high places.