It depends on the sort of story! A lot of them were designed to explain things that we didn't have an explanation for at the time - how the world was created, why animals look or act the way they do, what makes things work in general! Before we had science to explain it, people had to come up with explanations that they could understand. People need to know how things work, it's just how they are!

While other stories are just for entertainment, or to teach morals in ways that are easy to remember and relate to! ...I think!