It all stems from class. It was okay to see a peasants nipples but not a ladies. That was quite unladylike. But was no uncommon for a peasant woman to walk around topless and no one would bat an eye lid. Naturally the prudes that are Victorians quashed this because it was quite vulgar.
However, the class reason still exists, which is why you can see third world titties on TV during the middle of the day and no censorship, but have to wait until after the watershed to see Western tits.