Because it's crass. Because of that asshole at the Skyrim demo who screamed out "rape her" as soon as a female character appeared on the screen, and that this kind of advertising, if you can call it that, appeals to exactly that demographic.
Other cultures can handle sexuality better. Americans, male and female, toggle between acting like a a pack of feral dogs and a congregation of calvinists whenever the subject comes up.
In my personal experience, the Scandinavian cultures do it better by simply not making a big deal out of it.
When you teach all your children from a young age that nudity is naughty and sexuality doesn't exist, you shouldn't be surprised when they grow up ill equipped to handle such things maturely.
I am from Scandinavia and that's not really true. We like naked females as much as everybody else and will do as many stupid things to get them. What we don't have is a bunch of extremely religious people with power so the contrast makes it seem more easy going.
Other cultures can handle sexuality better. Americans, male and female, toggle between acting like a a pack of feral dogs and a congregation of calvinists whenever the subject comes up.