The simpler explanation is an evolutionary memetic one. Thousands of creation stories were told around campfires for thousands of years. As communication among tribes improved, the stories whittled down. Some story parts propogated and some died off.
Then some cultures developed written records and the variants trimmed some more. Then came fixed type, and the deed was done, trimming the major survivors to a mere handful.
Most people assume that the theology, say the 10 Commandments, established our cultural morality. My contention is that the theology usually just confirmed an evolved, survival-based, moral social compact.
I use Buddhism as a case in point. What kind of "survival ethic language" will propagate and survive when basically life is shit and hopeless for most people? Buddhism fits this bill well.