This of course has a rather obvious explanation, but HN prohibits mentioning it for political reasons.
A movie full of violence won't sell as well in Germany. It isn't want Germans want to go see. Vice versa for Americans and sex.
Culture dictates what kind of media is desirable, not the other way around.
Again, the cultural aspect is core to the entire thing, but nevertheless the overarching theme is that both countries apply a sort of self censorship.
Every country has something that rates or censors entertainment for popular consumption. Some are overbearing or carry criminal offenses (Iran, Russia) and some are more off economic (store wont sell your game).
Germany became strongly anti-violence after WWII cause the normalization of violence in that period and level of it was extraordinary high in Germany.
Both of these are completely misguided (IMO) moral policing and disempowering of the population. Both say: people are not capable of making a sound moral choice on their own, they must be protected from seeing things that could negatively influence their character.
That being said, if I were to pick between these two bad policies, I personally think sex is a vastly less morally objectionable topic. On one hand you have an activity that (between consenting people) is pleasurable and is essential in propagating the species, while the other is generally undesirable to everyone involved.