I've always felt that the appeal, at least for me, is that there is a tiny—or maybe not so tiny—bit of each of us in those photographs. An uncomfortable familiarity that you can't quite put your finger on. Nor do you even really want to. But you look anyway because something out in all that darkness rings ever so slightly true.
You may not have actually been there and done that. But at some uncomfortable point in your life you may not have been all that far away either.