Religion

GOD is an acronym for Guaranteed Overnight Delivery, and a bit of a misnomer at that, because while the bible does record that he occasionally delivered people, it wasn't guaranteed, but rather contingent on their obeying a number of strict commandments. And overnight? Not even close. 40 years wandering in a desert doesn't count as overnight, even by extremely lax USPS standards. This kind of shoddy service is why startup religions with more diverse delivery systems will gain popularity in the coming years.

Honestly, polytheism is just cooler anyway. It's for the same reason the X-men are cooler than Superman will ever be. People want demigods with humanizing flaws, and personalities, and specialties. One quasi-omnipotent being can't have any useful interactions, and there's simply no opportunity for empathy.