Why is nudity such a big deal?

in the US, at least (i know other cultures tend to be more open about it). first off, we all used to be naked/scantily clad back when we were cavemen, right? it’s natural, it’s normal. sure, climate and social standards nowadays have hindered peoples’ freedom to be sans clothing, but come on! why do i remember janet jackson’s nipple slip at the superbowl better than who actually won it? why can we walk around in a bathing suit on the beach but not in our underwear down the sidewalk? why are people so afraid of the human body? if it’s such an amazing thing, why is it so taboo to see it?