Here’s the thing, society formed around agrarian settlements. What do you need for crops, livestock, AND people? What makes transporting your goods easier? If you said water, you get a prize. Many of our settlements, both modern and historic, were near water sources. Water sources flood. Inevitably, water sources experience thousand-year flood events, and completely swamp a huge area, maybe even wiping out one or more settlements. As you start going back in history, you also start dealing with glacial dam rupture events, which also almost certainly scoured away everything downstream and would have seemingly come out of nowhere at all.

The phenomenon of the global flood myth is really just that people live near water, and when you live near water, shit happens.