That's not true. Actually, most hide the fact that they have it because they don't like it. It makes them feel different and weird. Like something is wrong with them.
Well obviously something is wrong with them if they're slicing their wrists and wanting attention for it.
They want attention? That's why they will go to extreme lengths to hide it, just to get attention? You are not them. You don't know what thoughts they battle in their minds. It can be a very scary place for them. And obviously, something must be wrong with you for judging what you do not understand.