jb, that's similar to why I'm going to occupational therapy as a career to specifically work with autistic/developmental disabled kids. I went through crap as a kid cuz no one understood what my 'issues' were, I was just stuck in my own world and no one could get me out of it. There's so much that I feel I can do to help kids avoid the pain i went through by not understanding what was going on, so I want to be there to help them. And OT is a great way for me to do that.
I suspect the above is a similar situation to why T's go into therapy as a career. They probably faced similar issues themselves and saw just how it felt to both go through it yourself, as well as help someone else through their issues.

Course that's not to say that's for everyone. But it's a possible explanation for some.