Earlier quoted context omitted.
The Ziz method of indoctrination involves convincing his minions they are trapped inside a mental framework they need to break free of. Trans people already feel trapped in a body not aligned with who they are, and are naturally susceptible to this message (and therefore natural targets for recruitment).
Following on because the edit window elapsed, the specific method of indoctrination used by ziz (but invented by Gwen) involved in novel method of sleep deprivation to induce split personalities. It’s been called “installing demons.” I wouldn’t be surprised either if the causality is the other way around: Ziz reworked these people to be trans. Ziz certainly seems to have treated the minds of the people around him/her…
There is some precedent; the Twin Flame cult coerced transition in some members if I remember correctly. My guess is it was emotional manipulation used to make them do something that makes them more vulnerable to control. If you transition and you are not trans, you are going to have a hell of a lot of dysphoria, and shaming people and telling them it's because they are not trying hard enough/a good enough person/etc. would absolutely make it hard to break away.