User blog comment:B214/Question and Answers 6/@comment-24098614-20161212223522/@comment-29963364-20161212230537

I think the "soul stealing" was just a way to spite the Biblical God, and get humans to become subservient to the Devils (selling your soul to the Devil could also mean becoming the Devil's slave).

But after the Great War, and the creation of the Evil Pieces, Devils no longer wanted or needed to steal human souls.