One reason I believe American culture has become so vulgar is that people have realized that there are a few things that appeal to everyone: sex, violence, and intrigue. Some of the most popular video games, for example, have all three elements, though most will downplay the sex since most violent games are for teen boys.
The most popular movies of the year often have a rating of “restricted”, or R, due to violence, language, or sex. One of the most popular bookseries in the last 10 years was Fifty Shades of Grey. Movies were made, and they were also popular.
American culture is vulgar only in that there is no shame in anything anymore. In some ways, this is a good thing. In many others, it is not.