‘So why doesn’t God overlook all sin?’
overlooking sin is one thing; an onmiscient entity destroying his entire living creation (as you recall, all animals and children, including the unborn, were wiped out as well due to what God determined was his own mistake in creating them in the first place...before invoking the concept of justice, please explain how destroying those who cannot by definition live in sin (animals, infants) for their sinful lives in any way describes any notion of justice...
Human beings need to understand that their evil destroys not only themselves, but also the creation over which The Creator has granted them dominion.