I figured it was sort of like what you first said, where everyone has very different opinions and thoughts about their religion. Everyone claims that theirs is true, other people are false, etc etc. I'd imagine that the gods themselves still require mortal worship to maintain their power, or at least to use their concepts for those who aren't exactly worshiped commonly anymore. Sure you might not believe in a sun god, but you still need the sun, and in doing so you put a bit of faith that the sun keeps doing as the sun does and it gives the various sun gods some faith. It's a bit trickier with more metaphorical concepts like hell, but giving how many people want to send their undesirables there, I'm sure Satan doesn't have to worry about people not believing that he or his domain exist.