“The Earth was created in 4000 B.C., and the Great Deluge therefore occurred in 2,000 B.C., or thereabouts. This shocked the living hell out of the Egyptians who already had a thriving civilization going at the time. It pissed them off so badly that within a few years of the flood’s having receded, they’d completely rebuilt their civilization and pretended that the whole thing had never happened.”

That would be the proper answer.