.
There are very few "blank slate" Ts. In fact traditional psychoanalysis actually does involve interaction with the T and a very close relationship develops.

The issue is really invasion of a Ts space and privacy.
Knowing if they like coffee is one thing, knowing about their family life, their struggles, their divorces, is another.

Another issue is if it comes directly from the T versus a client driving by their home and looking at their plants or if they have toys in the yard, etc.
Invading their space is a boundary issue and almost disrespectful.

T's are not our friends. They are doing a job, and the goal of their job is to focus on the client. Look at all the stress talking about themselves brings people when they find out something about their T that is different than the client imagined or wanted or envisioned.

Infants don't attach through conversation. Infants attach through eye contact, soothing responses, and being relieved from their stress. T's provide that through empathy, understanding, repeating what the client says so they feel heard, etc. A T does not need to share their lives to create attachment.