When Satan lost to God, his wings were cut off and he changed from an angel to a demon. After being reborn in the fire of purgatory, he led the fallen angels to build a devil's paradise in the dark place.
They can be happy and free.
Heaven is not an ideal paradise, it has countless constraints; angels are burdened with too many missions, and they are not happy. Then countless angels fell, and they were called "Lost Angels".
Hundreds, thousands, ten thousand years, we are just looking for... The lost paradise.