The US was founded by some crazy cult members who had extreme views about sex. The Mormons came out of such a cult, but were pushed out of the country. Most of those old cults are still around to this day.

The religious views from these cults lingers on in our social conscience, probably most notable in our sexual repression and sexual censorship. Those old cult views instilled the idea that sex was depraved and not something to cherish and enjoy. So we still, at least subconsciously, hide sexuality out of a sense of righteousness and politeness.