It may just be simply an issue of biblical exegesis. One scholar writes:
critical issue in the Flood story in the King James Bible has to do with translations of the Hebrew words eretz and adamah as meaning the entire โearth.โ What do these terms actually mean? It is widely recognized that Hebrew is a wonderful language for poets, since virtually every word has multiple meanings. But that same characteristic makes it a horrible language for precision. As it turns out, eretz and adamah can indeed be a geographical reference akin to what we usually mean by โthe earth.โ But it is not at all clear that the ancients had the concept of a spherical planet that you and I do. Many scholars argue that the Bible writers thought in terms of a flat earth that was covered by a bowl-shaped firmament into which the windows of heaven were literally cut....
Duane E. Jeffrey
Commenting on this, one reviewer added: "Jeffrey notes that ideas of a global flood may have resulted from a widespread local problem. A current hypothesis that has been gaining ground since 1998 is that a significant flooding event occurred in the area now occupied by the Black Sea. Evidence has been discovered which has led a number of researchers to believe that the Black Sea area was once occupied by a completely isolated freshwater lake at a much lower level than the ocean. The theory is that the sea level rose and eventually broke through the Bosporus shelf, resulting in a rapid flooding event which would have wiped out all life living along the shores of the lake. Whether this is the source for the Genesis flood remains conjecture."
Although no certain evidence for the flood as a global event has been forthcoming, it's interesting to note that the legend of the flood exists in almost all the cultures of the earth, from Greece and Rome to Asia to the New World.