D&D's main setting is built as a kitchen sink with tons of weird conflicting ideas happening at once so that people can exclude whatever parts they want to create their coherent setting. You want to do a vampire story? A tolkien-esque quest? Steampunk? Wizards of the Coast is happy to sell you rules for all of that.
This is the core weakness and strength of the Forgotten Realms. It has everything but if you think about it nothing makes sense. Paizo did the same with Golarion, probably because they saw that the versatility of settings like FR more than make up for the lack in coherency.
