Which part of the United States? I'm the UK so have no first hand experience but the impression I get is that New York and California are pretty liberal and that other areas are rather conservative. I also suspect there will be the same difference between the city and rural areas.
Likewise, in Europe, there are differences. The Dutch and the Scandinavians are known for being especially liberal. Years ago it was a big joke here in the UK how brash the Scandinavians were talking about sex but what that actually amounted to was that there wasn't even a hint of taboo about it - they saw it that bodies are just natural and sex is just one of the things people do just like eating, sleeping or working.
Then here in the UK, which is part of Europe geogrpahically even if we have just left the EU, things are somewhere in between. We have been steadily becoming more liberal, certainly since the days of "No sex, please, we're British", and are almost certainly more liberal than much of the USA. I don't think, for example, a woman's "wardrobe malfunction" on live TV caused quite the same fuss here.
But as to the reason, probably religion. To a first approximation the pilgrim fathers who left for America from England did so because England wasn't puritan enough for them.