@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.
@colonelj @georgia
I kinda thought it'd be that way.
Here's what I think. The issue might be that there are 2 conflicting worldviews that trans-women have.
1) The general trans view that the two sexes/genders have traits that are quite different from one another, to where having traits of the opposite sex/gender makes you dysphoric.
2) Feminism, that states there are no fundamental differences between sexes/genders, and eventually ends up punishing masculinity in men and femininity in women as a consequence of denying these differences.
So imagine a trans-woman, that for whatever biological fluke can't connect with her male body and doesn't feel masculine, but is also taught to reject femininity, that femininity has nothing to do with womanhood, and even attempting to state that it does is bigotry.
So you have a trans-woman, that probably feels inherently feminine, but is also discouraged from expressing it. So she can't form a real identity for herself. All she is allowed to have is "trans".
Maybe this is also why other "identities" like non-binary and genderfluid have started to pop up.