After thousands of years of teaching humans to see the Anu as Gods and to worship and obey the Gods, it was dangerous for those of the military who had all the power to let so many of their banished kindred roam the Earth unchecked.
And so, history was written by the victors.
Humanity was told that there had been a battle in heaven, and that some of the lesser divine beings (sometimes known as Angels) had rebelled and would no longer obey the Gods. They were told that the rebels were dark, scary and evil, of the devil, and always lied in everything they said – and that the Gods had punished them by casting them out of heaven to a horrible place of pain and darkness.