I think it's a combination of access to the LGB activist infrastructure, the overrepresentation of transwomen in tech, and the way in which TRA activism becomes a socially acceptable form of misogyny. It's hard not to notice that there is an overlap between incel/MRA rhetoric and TRA rhetoric and that some transwomen writers literally were MRAs who decided to transition.

Also, it's an easy way for men to feel progressive without having to sacrifice anything. I think it was Dr. Stock who wrote an article about this in regards to philosophy. For the most part, transmen are not able to redefine man or access male spaces in the way transwomen are doing the reverse (hmm... I wonder why that could be?)

I also think that whether by accident or design, the movement was smart in how it burst into wider public view. As I saw it, the bathroom bills were what propelled trans-rights into national consciousness. It instantly aligned progressive politics with trans advocacy and was sympathetic... people just wanted to pee. Who could argue with that? Especially because (I think) most people assumed that transmen and transwomen were like what we saw up through 2010... primarily same-sex oriented people who medically transitioned as best as they could to try and then lead perfectly ordinary lives as the opposite sex. The trans kids furthered that impression because kids are sympathetic and their lives are very medicalized. We didn't know that Tumblr was busy promoting the idea that biological sex isn't real or how much work was being done to dismantle safeguarding requirements. By the time it became impossible to ignore that, social media had already baked in that part of progressive identity was trans advocacy with no questions or qualms.

It also doesn't help that it is very difficult to talk about the issues with transvestic fetishization or AGP without sounding transphobic. I don't know how to get around the fact.