ELI5: How come plenty of deities in different ancient polytheist civilisations had more than one association?

For example, Zeus was known as the sky god and the god of lightning but Athena was the goddess of wisdom, knowledge, war strategy, craftsmanship and so on.

Same other ancient civilisations such as Ra was the Egyptian god of the sun while Seth was the god of chaos, violence, confusion, anarchy, war and so on.

Since ancient civilisations shared similar ideologies (like different city-states in ancient Greece shared a similar belief of the Olympian Pantheon), how come did they did not manage to come together what gods associated with what?