Because the history is not repeatable, to an extent it is speculation, but from what the bible says, there was more water in the atmosphere then than now, as well as super-hot water coming from beneath the earth, and it is easy to show water exists beneath the earth.
It's important to take a look of a map of the globe without any water on it. The mid-oceanic ridge is much more explainable given a massive catastrophism, IMO, in that this explains the continents splitting. You can trace the continents being split by the ridge.
If you look at the continental shelves, there are double continental shelves visible.
I have not dug too deeply into this topic personally, but I do not think that it is a big problem, it is certainly credulous compared to a rock sprouting feelers, for example, whereby such a proposal is completely invented, 100% speculation, without any facts to look at.
Believing in a flood is not as big a deal as evolutionists want to make out. We also believe that life produces life. Abiogenesis, I would say, take much more faith to believe in, than a large flood, which is not just possible but easily probable.
These are my own opinions more than arguments, from the explanation I deem the best one.
I think the fossils, the continents, super-hot water, preservations of polystrate fossils, preservations of a vast number of kinds that have extant counterparts today, well......basically I don't see any problem as to why a flood is not conceivable. I won't argue this any more than I would argue that we breathe in oxygen and breathe out carbon dioxide, it is futile.
The reasonings against a flood I deem pretty tenuous. They are invented to thwart the flood rather than coming from any genuine attempt to falsify it. At the end of the day, for me it is much more reasonable to believe life comes from life and that X produces X, as the facts clearly show.
It should also be noted that the attitude that there can't be any supernatural answers for the problem is decidedly odd, considering it was a miraculous event, according to the bible. To have us believe that God would create a flood but could not then handle the consequences and therefore not be able to save a remnant of life on earth I regard as absurd.
Edited by mike the wiz, : No reason given.