I only speak for myself, trisher, rather than make assumptions that are not backed up with figures. Of course I can't explain why sex scenes are there! I can give an opinion, but it would be just that, the same as yours is.
FWIW, I would guess that film makers try to appeal to as many people as possible, so in most big-budget drama there is some sex, some action scenes, some romance and so on. That is not the same as people 'demanding' sex scenes. People went to the cinema in the days when actors had to have a foot on the floor when a couple were in bed.
I agree that the protection of young women is important, which is why it is 100% the right thing to hold the perpetrators of assault, abuse or other bad behaviour to account and use the full weight of the law when necessary. I don't think it is fair to those young women to shift the blame from the perpetrators to 'the public' for not switching off when a naked body appears on their screen in case it gives implicit approval to its inclusion.
Also, your dismissal of Gransnetters is rather dismissive. We are a multi-faceted group, and I'm sure that individually and collectively we do make up a significant part of various audiences, and as such will be of interest to programme and film makers.