At the same time, they picked and chose what they wanted to from those stories. They themselves tried to redefine some things and evolve, little by little. Same goes even for their conception of God. Or even the afterlife (or lack thereof.. Judaism originally didn't have an afterlife.. it had the "grave" - Sheol). As for God, there wasn't really a tradition of "Yahweh" at first. It was just Elohim (God or Gods, in the generic sense.. as we use today). From Elohim, it evolved into a patriarchal kind of thing, where they started referencing this God as the "God of your fathers, the God of Abraham, Isaac, Jacob". Then the Levitic/Moses period started using a proper name. And even after that, the David period started centering the religion on the city and temple of Jerusalem specifically. And so on and so forth. Christianity is another extension and evolution of the region's history. Nothing is ever written in stone (of course, very few would agree with that now.. people are fixated on the "unalterable Word of God".. but religion itself has shown to be a living tradition. Not a written one).
edit: I don't mean to limit my example to just that religion. Buddhism could be used as an example that changes over time and according to region.