I understand. I am sorry for your struggles in understanding what he needs and what would help. It is of course a very complex problem - why people do not do well. But I do believe psychiatry is part of creating the problem. People get lost in their "illnesses" - sometimes for life.
There can for sure be biological reasons - our brains are very complex - there can be anything from brain damage to all kinds of alterations.
I am sorry if I sound like I have the answer to all that are suffering. I of course do not. But what I do know - is that many that are deemed mentally ill - do have loads of trauma.