Because most of Tyson's opponents were beaten by fear before the bell for the first round rang. Remember what Tony Tubbs said to his corner at the end of the first round vs Tyson? "Damn, I made thru the round".
Mike Tyson is either vastly underrated or vastly overrated. In this instance he's the former. He's at least two tiers above Jerry Quarry.
That poster is no longer here. While Floyd and Mike had similar styles the latter packed infinitely more wallop.