Your own claims contradict this argument. You are claiming that a supernatural flood would leave sediments just like a natural flood would.
For the same reason that they abandoned the previously widely held belief that the Sun moved about the Earth in a circular orbit.
Yes, any flood of water we can observe leaves evidence including sediments. I see no reason to presume a Supernatural flood would not leave sediments, but Omnipotence rather implies He could do that if He wanted to - Supernatural supervac I guess. And Omnipotence would be the point of saying if there was a Supernatural global flood there is no reason to suggest the layer of sediments deposited must appear exactly as it would in a natural flood.
If the flood Noah experienced was natural, what would be the point of saying God did it?
So yes, sediments everywhere. Even science agrees at one time or another, often multiple times we can point to what appears to us as obviously a presence of water being over what we observe now. Even if we have to point to where the sediment covering a particular bedrock that is now exposed went, we have found where it went and so can say we know it appears sediment was deposited there at one time or another. If I recall correctly there is a great plains to Grand Canyon example of this, forget what it is called, said to be like a trail of sediment layer formerly covering bedrock now exposed in Canada, New England and I think even from across the Atlantic.
Anyway, the disagreement only comes about because science claims layers of sediment being laid down in the manner they appear now to us, cannot be attributed in any UNDERSTANDABLE way to a naturally occurring global flood. Am not in disagreement there as I am not talking about a natural event.
Conflating wrong ideas with a matter of faith is not particularly hard to do or convincing. Many cultures expressed the movement of heavenly bodies as they appeared, we still talk today as if the sun "rises" and "sets". So it can hardly be said such expression always indicates anything more than a belief in what we can observe. As our observations got keener and our abilities better, those beliefs were corrected. Geologist have long ago been telling us there is no evidence of a natural global flood. The OP specifically asks why within our lifetime have Christians abandoned what was practically universal in my childhood. There have been no great geological discovers banishing a natural global flood in my lifetime - that concept was pretty well dashed before I existed. It actually started not long after the first person observed that evidence of aquatic life can be found practically everywhere on dry land.