That is the truly fascinating question. I've seen many possible but partial answers on the level of countries:
Working behind the curtain, piggybacking on some other social justice movement (self-ID bundled with same sex marriage in legalisation, say), and being funded by a handful of very very rich trans activists.
But then for years the question of transgender women in women's elite sports was discussed in committees and meetings where women were not invited at all, and this example, I think, is part of the explanation:
Almost all the negative consequences of these policies fall on the female sex, and most decision-makers everywhere are still predominantly of the male sex. Almost none of the harm would affect them directly and some of the changes actually benefit them.
When you add that to the virtue signaling you might get the kinds of examples we can observe in the academia, too, especially as the gender identity ideology states that women are privileged compared to trans women, so that it is the former who should always been viewed as the underdogs, even if the woman is, say, a black Lesbian.