Mary died in a fire, because the family was attacked by an ifrit not because of a demon. There is no Apocalypse looming in the near future in this AU.
Plenty of hunters are polytheists, but the Winchester and the Campbell clans have always been monotheists and believing in anything other than the One is wrong. Dean has never believed in anything, much to the disgust of his very strict monotheistic father. His sudden step toward paganism would be greatly frowned upon if anyone in his family knew. Sam is more opening minded when it comes to pagan worship, but he is a faithful monotheist.
The Samulet is a powerful pagan talisman for channeling divine power. Sam didn't know this at the time that he gave it to Dean. Bobby had only said it was unique and that his father might benefit from its protective properties. Dean has worn it for so long that no one thinks twice about it.