Why can a writer engage in sexual imagery with no restrictions and yet a film author can't do the same?

When I was at university, the film club always showed In the Realm of the Senses (Ai no korîda (1976)) at the start of a new year to get people to join. It was full of explicit sex, yet you can buy it in HMV now.

Cinema has been extremely conservative and prudish. I wanted to go to the opposite extreme and show the relationship only through sex. [on 9 Songs (2004)]

I don't particularly like the idea that there's an arc to the story and that therefore in this scene you have to convey this bit of information or emotion. I like more the feeling that, of course, there is a shape to the story, but that each scene should feel right, should be true at that moment, and that gradually you accumulate these moments of truth until you get enough of them together that it becomes a story that's interesting.