If you are asking, is it possible there was ever a great, world wide flood? The short answer is not likely.

There are two points working against a great, world wide flood. First, where did all the water come from and where did it go? More scientifically, an event of such magnitude would almost certainly leave a sediment record. There is no record in any geology or core sampling of such an event.

As for why the ubiquity of the story? Several reasons contribute. First, flooding is a world wide phenomenon. Second, catastrophic flooding is not unique. There are theories that may 8,000-12,000 years ago the Black Sea was land locked, with a very small passage for water. Early settlements established on the then shores. However, the damn broke and the Mediterranean flooded in and washed away all the settlements/cities on the banks. This is essentially what is represented in the Epic of Gilgamesh. Archaeologists have found settlements well underwater in the Black Sea supporting a sudden and catastrophic rise in water levels through out the Black Sea area. Similar site have been found elsewhere. There's evidence that northwest Europe saw a similar sudden rise in sea levels thousands of years ago. Archaeologists have found settlements well into the North Sea. but, flooding of all types is a world wide phenomenon. So, it isn't unusual to see stories about it. Furthermore, prior to the establishment of large enduring empires, when most societies were tied to city states which were usually on a river or coast, a massive flooding really might wipe out your "whole world."

The other reason is simply the transfer of idea. The Epic of Gilgamesh was Assyrian/Babylonian. So, how'd they hear about a story from the Black Sea? And, very importantly, that story is generally recognized by scholars as the source of the Flood Story in Genesis. So, the Story moves from Northern Turkey to Mesopotamia to the Levant, and from there, via the Torah, Bible and Islam, to the whole world.