I was a radical trans person before I detransitioned and got into transphobic radical feminism. Hung out with radical queer and trans people, went to Camp Trans, read plenty of books by trans people, knew all the counter-arguments to transphobic feminist beliefs, etc.
Before I become one, I used to think transphobic rad fems were totally out of touch with reality. Couldn't understand why they thought trans people were in league with the patriarchy. I used to hate read rad fems for years because I found them so ridiculous.
Transphobic feminism only became compelling after I went through several disruptive events in my life and it started to seem like it could fulfill my needs. A huge factor was that conflict had ripped through my personal community and I no longer felt like I could trust people.
My old community no longer felt safe, so I was on the look out for a new one that could meet my needs. I was questioning my gender and unsure of how to live as a woman after living for years as a trans dude. I also was quitting drugs and trying to work through old trauma.
Basically I was going through a lot, in an emotionally vulnerable place, my old community/support system had been disrupted and I was pissed about it, I wanted to detransition but didn't know what that would look like.