Why didn't DIO used his piercing eye attack to kill Joseph or Jotaro? When DIO stops time to kill Joseph, he uses a knife. But why didn't he use his piercing eye attack? The same goes for when fighting Jotaro: he doesn't use it and uses a police officer's gun or knives instead.
My real-world explanation is simply that Araki forgot. However, my lore-friendly answer is that Dio either wasn't capable of using his Vampiric abilities because of Jonathan's body, or that he simply didn't care to because he was virtually invincible with The World.