The old world was undone by substantive moral disingenuousness.  The people of the old world sold themselves into dark sexual perversity.  They stepped out beyond the sexual addiction myth, and gained carnal knowledge of a forbidded nature.  They were subsequently washed away due to their extremely polluted nature.  Their catastrophic fate became an enduring motif of what happens to those who shun the divine will, and follow lust patterns that can never be satiated.