Genesis presents a unique theory: the creation of all things by a single creator. Babylonian, Greek, and Roman mythology did not posit this at all. So the question is: where did the idea come from?
The civilization was large enough to implement many different worldviews. Some of them were weaker and died out. Some of them were stronger and they survived. A church of a single creator is unified and as such is stronger than a bunch of temples of different Gods, each with their own mini-religion.
“the question is: where did the idea come from?”
The nature of the answer to your question depends on whether or not the idea is true.
Sure, one has the right to claim the idea that God created the universe is a myth and then to establish this as a premise—as your question appears to do—but we must remember there is no logical or empirical proof that it’s a myth.
Therefore, one possible answer to your question, one completely consistent with logic, is that the idea came from God when he actually did the thing.
“the question is: where did the idea come from?”
The nature of the answer to your question depends on whether or not the idea is true.
Sure, one has the right to claim the idea that God created the universe is a myth and then to establish this as a premise—as your question appears to do—but we must remember there is no logical or empirical proof that it’s a myth.
Therefore, one possible answer to your question, one completely consistent with logic, is that the idea came from God when he actually did the thing.