But the US is far from the only country that's so sensitive about it. Pornography in China is forbidden, in India is very iffy. In Islamic countries it can be extremely illegal.
Even in the Netherlands where I'm from movies have become a lot more prudish since the 70s/80s.
Wasn't even considered sexual content, and in no way shielded from kids either. The context isn't sexual, and it's a perfectly normal body part.
The sexualization of the human body is nothing but a cultural invention.
Somehow the sexual revolution of the 60s/70s running out of steam, and a correction taking place. A growing influence of American culture as well as Muslim immigrants, both more conservative. And perhaps feminism changing course.