I think it might have to do with the type of therapy. I'm in behavior therapy and my T often uses examples from her own life that relate to my experiences/problems, from which I've learned many details about her. She also said that if I were for example seeing a psychoanalyst, the type of questions asked would be different and the T would probably not disclose as much or try to be as "equal" to the patient.

If it's not that, maybe it's just each T's individuality.