Social pressure can get most of the people to conform most of the time, but not all people. In any oppressive regime, for example, there’s always a resistance. In the Asch conformity experiments, many people gave obviously wrong answers in response to social pressure, but a minority didn’t.
Once a person has committed to transitioning, it’s natural for their behavior to continue down that path--they are giving themselves permission to do so.
Earlier in life, I tried to be more gender conforming: shopping for dresses after work, cooking and cleaning, entertaining my partner's friends...I didn't have time to read or write and felt I had even lost my ability for creative thought. Then I reversed strategy and gave myself permission to read and write and think in a more unconventional way. By engaging in those activities, I became a more original thinker again. It certainly feels like my brain changed in response to my daily activities, even if I didn’t get “before and after" brain scans.