One: Social identity: tatoos and piercings, orange hair and proud sexual perversity (and, getting there, branding) are passe. Cutting is the next step, to push the envelope.
Two: Sympathy junkies. A rational result of the victim industry. Normal? Nobody give a s**t. Screwed up: "we care more". The attention is toxic.
Cutting is not something kids show to others, they hide it. It is something they do because they learn about it from friends. It feeds some strong needs and provides one heck of an endorphine kick.
Its addictive, and kids have a hard time stopping once they have tried it.
If you ever have the misfortune of having to deal with this, you better change your attitude.
The smart parent digs quick to find what is driving this and root it out like weeds in the garden. Then you have to watch and supervise as they find better ways of coping.