Actually there is evidence of a mass flooding, just not as widely agreed upon as to how large it was.
Flood geology

Proponents of flood geology contend that the Biblical account of the global Great Flood is to be taken literally in which most observed geological processes, like fossilization and sedimentary strata, are a later result of this perceived divine event.

While many people hold the belief there was a worldwide flood, flood geology itself has been unequivocally rejected by mainstream geologists, many of whom consider it a form of pseudoscience.[24] Though at one time even prominent workers in Biblical archaeology were willing to argue support for flood geology,[25][26] this view is no longer widely held.[27]

As to why they disagree now I don't know, but there is all sorts of evidence that shows geological wear caused only by water across globe and it's pretty consistent. It also happens to be the layer in which most fossils are found.