I think it's just part of a decades-long trend (with the last fifteen years seeing an acceleration) toward overt sexuality in dressing (and conversation and actions) becoming, not only acceptable, but prevalent in society.
It goes back a whole lot longer then that! Just look at upper class women's clothing from the 18th century. Every thing being forced up and out of the dress! Talk about two eyes full. I don't know about you, but, I'm really glad the codpiece went out of style!