I have noticed this fetish becoming more popular the last year or so myself, I guess some people are turned on when a girl leaves her clothes on because maybe it adds to the level of mystery to the scene. Sometimes one of the best parts of a scene is seeing a beautiful girl in a sexy outfit as she teases for the camera, because you're anticipating the clothes being taken off and her body being revealed. I have come across a few scenes where the buildup of a scene was awesome because the girl in the scene looked so sexy in her clothes. Maybe there is a "reality" turn on to it as well...
Looking forward to seeing other opinions on this topic.