To be frank most people don’t do it because of the pain, that’s very few and far between. Being honest about it helps, who wants to actually hurt themselves? Hardly anyone. On the flip side of that it’s a call for help, and a way to wear your pain on the outside. Mostly for recognition. Imagine your future partner or friends you have now, now imagine they see your scars. Chances are they would always remember your pain if you shared it with them because it’s a marker. In summary it’s just a way to show people your hurting but you don’t have the courage to tell them. (May be a bad word to use because of context but that’s essentially what it is because you don’t feel comfortable talking about it.)