To some degree that's a compromise. There are people who want neither nudity nor violence on TV, but they've lost the violence fight (somewhat: there are still limits, see http://screencrush.com/avengers-rated-r/ ), while winning the nudity fight.

Often when laws don't make sense, you'll find the law was forged as a compromise, rather than a logical overmind creating it. the constitution is a clear example of this.