I think another reason is that the female body is more "beautiful" than the male. We are the "softer sex"- don't forget.
I mean, I'm a straight woman who loves men, but even I do not want to see a fully nude man shakin' it on a stage or in a movie or magazine or whatever. In fact, I'd probably be completely repulsed. But a fully naked woman isn't disgusting to most people. Just from a purely superficial viewpoint, I think a woman's body is more beautiful than a man's. I think many people share that opinion. There is something. I am sure it's society and conditioning, but I think that is a factor.

Also, why would men want to see men get it on? They'd rather see women. And men buy magazines, watch those kinds of shoes, etc. much much more than women. So they are the target demographic.

I'm personally not offended by any of it.