Therapists have to have strong boundaries. I am a LMSW and one of the first things you learn is how to maintain those boundaries. Not just for liability reasons but to maintain a professional, unbiased approach. And last but not least, if you don't maintain boundaries you wind up 'taking your work home with you' and it's too hard to lead a healthy and satisfying non work life. That's one of the reasons people get burnt out and quit (even when they set boundaries). People forget that therapists, pdocs, social workers are all human too and it can be really emotionally draining.
The therapy is there for you, not the therapist, so the less they talk about themselves the better.