Because that's what everyone took offense to. That's what the normies disliked about Biden the most out of everything in that debate. It wasn't the blatant lies that he never said what he said or any of that. They were all talking about that gaffe the next day. It's bizzare but we're talking about the people that elected Bush because he was cool to have a beer and picked Obama over Mittens because Mittens hates dogs.