Jamieson, Fausset and Brown on 2 Kings 12:3

3. But the high places were not taken away--The popular fondness for the private and disorderly rites performed in the groves and recesses of hills was so inveterate that even the most powerful monarchs had been unable to accomplish their suppression; no wonder that in the early reign of a young king, and after the gross irregularities that had been allowed during the maladministration of Athaliah, the difficulty of putting an end to the superstitions associated with "the high places" was greatly increased.