It's literally something that helps maintain a physical aspect associated with a person's gender. Granted, hairloss can happen to anybody, but baldness is highly predominant towards the male population.
It doesn't really make any sense to say that preventing a natural feature of men from progressing is being done to affirm men.
I have man boobs, I guess fixing that would technically be gender affirming care because I'm embarrassed of having female features, but balding is really a stretch.