Ahab and Jezebel made Baal worship the state religion.  Baal worship is an adaptable religion - it encourages the worshipper to gratify his desires.  By contrast, God calls his worshippers to die to themselves and to live a godly life.  On Mount Carmel, God proved that he was the true God and that Baal was powerless but idol worship continued because Baal allowed them to worship themselves.