Many women do more than that when they're alone with themselves. But the contrived rules do not allow them to relax with a partner. It is not without reason they say, that a smart woman has it in her head, a fool has it in her mouth. I even know men who categorically reject such liberties.
It's pretty much clear with sex, even using a condom. What is not clear is why there are two big TV sets on the wall practically right next to each other. And what's more, they are mounted at different angles! By the way, the man can clearly see how much he enjoys his girlfriend. Although to be honest she looks like a plank!