@georgia
From what I can tell it's partly a trans-inclusive thing (although this brings the obvious question of why is it that we only care about trans-women and not trans-men), but it's also an issue of feminists finding the word "female" insulting/offensive/dehumanizing somehow. Don't ask me why, it's just something I've noticed and don't fully understand myself.
@georgia
Another way of seeing things is through the idea that societies are generally gynophilic. So people will pay more attention to the feelings of women than men's. In the trans-women case, it's gonna be the people who don't see a significant difference between females and trans-women.
A potential consequence is that people who do think there's a significant difference, will focus on the fear of cis women, and will reinforce and enable those sentiments, drawing even more attention to this topic.