I think that as girls in US culture approach puberty they suddenly realize that being a more-or-less generic young person will no longer allow them to maintain

I think that as girls in US culture approach puberty they suddenly realize that being a more-or-less generic young person will no longer allow them to maintain an acceptable status. They feel the pressure to dress and do their hair and own nice outfits, etc. Some don't want to do that, period. Others sense that they will not be deemed attractive no matter how hard they try. They want to exit from the "game".