Are you asking a sincere question? Do you believe there might be an explanation you haven’t thought of?
I’m not a geologist, but this article does elude to the answer, and the Bible fills in the rest. Water came from the sky which wasn’t on the earth, water came from underground, and the earth looked much different than it does now. You know Mt Everest is growing right? The earth may have been basically flat. When water covered it, part of the crust broke and pushed some part lower and others higher. The water went into the lower parts.
What you describe seems like the theory of plate tectonics to me.