I cut myself often as a teenager and still do so occasionally.
Trying to explain why is complicated, because really there are a lot of dynamics involved.
When I did my first cut I never even considered the fact that anyone would see it... I was just finding life to be too painful and overwhelming and wondered what it would be like to cut my wrist... So I tried cutting near but not on the vein, just to know what it was like. At that point I had never even heard of "cutting"...
But when my boyfriend found the cut and I discovered his reaction, I kept cutting and the purpose changed. It did become "for (his) attention" in a way... It became a way of communicating my overwhelming pain in ways that I just couldn't through words... Because talking about my pain was just so incredibly hard for me. But even though it was manipulative and attention seeking and even though it unfairly hurt him... what people don't get is how REAL the hurt was and how truly close to death I had come within my mind... I really felt like nobody (except my imediate family) cared if I lived or died and I was so incredibly lonely... Everyone who was judging me were surrounded by more love and attention than I ever had, even when I did cut... I had to fight for what they recieved naturally... I guess it was my way of screaming to be heard, of saying, someone help me, I don't want to die but I can't go on hurting like this...
But obviously I got more out of it than that, since I still do it at times, and now when I do, I don't tell anybody... It just helps a little with the anxiety... It takes all my abstract, uncontrolable pain and makes it more concrete and bearable, in a way... I can't quite explain it, I know it's not healthy, but neither is holding everything in...
But yes, there's a huge lack of understanding out there with almost every mental health issue, and unfortunately hearing those things just tends to make our issues worse.