Myths have deep roots. My own realisation came when I read the Gilgamesh epic for the first time and suddenly there was Utnapishtim right in front of my nose. "Whoa, that looks familiar ... man builds boat to avoid flood. Heard that one before."
(At risk of teaching my granny to suck eggs, Gilgamesh is the hero of one of the first written stories. His adventures take him all over the place and at one point he visits Utnapishtim, who is the Mesopotamian version of Noah. Gilgamesh is described as two parts god and one part man and his battle with his own mortality is one of the core themes of the epic.)
There, I think, is the nub of the matter. With myth, we've all heard that one before. The stories and the way they work are part of how we operate as human beings.
If I was asked to define what makes people, people, I might well settle on stories and story telling as our defining characteristic. Plenty of mammals communicate to share valuable information, but I don't know of any other species that creates history and story for itself as the means to do it.
Stretching that a little further, I wonder at what point this happened. When did we first start telling stories around the fire? When did we first start trying to work out what happened after death? When did we first need heroes? It feels as if that was an evolutionary turning point. The need to know combined with the ability to put ourselves into another place or person.
Of course we still do it today. Drama and games in all their forms are part of this old tradition. We tell stories to keep ourselves human.