The theory of course is that the coastal people were the advanced ones and those inland pretty much primitives. The end comes and wipes out the coastal civilization that rose up and all that survive are a few refugees from the coast and the move in with the primitives and the primitives memorialize this in our mythology of their ancestors meeting gods or heroes. When put that way it's a plausible scenario.
-—The theory of course is that the coastal people were the advanced ones and those inland pretty much primitives-—
that concept is primary today except the interior people are known to dwell in flyover country
Why would everyday life have been transmitted in myth? The ice ages lasted thousands of years - it was all those people had ever experienced. Had it been summer one day, followed the next with mile-thick glaciers then that probably would have been remarked upon; but, as far as we know, the ice advanced and retreated over the course of centuries.