Well that's the thing, they talk about the same event otherwise they wouldn't share the same myth.
So if I saw I saw a flood on the flood plains at 6000 years ago, and someone else saw a flood 5000 years ago in India, you conclude they were the same flood, and happened globally?
We didnt lose anything. We have far better techniques now. It is like the myth that Roman's made better concrete. Just because we we often cheap out doesnt mean we cant.
We have seen such events over a far short time span, I think you are wrong. Natural disasters happen. Especially since the disasters those places had were common to their area.