Why don't any of the actresses have their pics on imdb?

If you look at the credits, you'll notice that the majority of the people shot in this movie have no picture with their profiles on imdb. Why?

Also, I need to mention that i did some <i>really</i> kinky *beep* in college (involving consenting adults) and watching the interviews has helped me feel less guilty. Cause some of that *beep* was downright naughty! Thanks, filmmakers.