Like many have said it is a cultural thing from experience and observation. Just to bring up some of the older writings on it, we also have the Epic of Gilgamesh and the Epic of Atra-Hasis. We also have the writing on the actual flood survival of Ziusudra.
Because we have so much evidence of Kangaroos, Polar Bears and Penguins hitch hiking to Israel at around about that time, so as to literally not miss the boat.
It's all part of the fantasy that must be believed.
Could say the same for the moon landing deniers, flat earthers, etc.
The bible says it, I believe it, that settles it.
@John_Tyrrell Yes, you're right, the bible ( Goat-herders Guide to the Galaxy) is 100% accurate when thrown from a distance of 3 feet or less.