Let he who is without sin cast the first stone. As it turns out, guys are just as guilty of posing in a cheese-on-toast way for their facebook profile pictures as the ladies are. Here's a breakdown of the usual suspects.
Advertising. It's there because we all believe in one way or another, even though we know it isn't really true, something inside of us wishes it was so. This is one rare occasion where it tells it like it is!
I suppose in Japan being a school girl is an occupational hazard, you don't know what deranged pervert will leap out at you. You've got Pedobear lurking about as well, so best to get tooled up, and where better place to put your weapon?