Adam Clarke on 2 Kings 23:9

The priests of the high places came not up - As these priests had offered sacrifices on the high places, though it was to the true God, yet they were not thought proper to be employed immediately about the temple; but as they were acknowledged to belong to the priesthood, they had a right to their support; therefore a portion of the tithes, offerings, and unleavened bread, shew-bread, etc., was appointed to them for their support. Thus they were treated as priests who had some infirmity which rendered it improper for them to minister at the altar. See Lev 21:17, etc., and particularly Lev 21:22, Lev 21:23.