Perhaps because transgenderism is a scientific human experience and that yes some people have brains more similar to their opposite sex.
To start to assess that, you first need to know what sex your test subjects are.
That's pretty easily established, because the differences between male and female bodies are usually unmistakable.
The differences between male and female brains, meanwhile, are indistinct and mostly a question of size.
www.sciencedaily.com/releases/2021/03/210325115316.htm
Why ignore the big obvious differences, and focus obsessively on tiny unclear ones?