Detransitioning stats can be a bit hard to get because of how easy it is to do depending on how far you have transitioned. For example for me, I'm pre-HRT so if I was to detransitioning it would involve cutting my hair, stop shaving my body hair, changing clothes and changing my name back. I, or anyone else in a similar situation, would never be caught in a survey looking at detransitioning.
And, surprise transphobes, not everything is supper permanent. Most things are pretty easily reversible. Even after HRT a lot of the changes are reversible. They just take more effort. The only things I'm aware of that are not very reversible are surgeries. Whichs why someone is usually pretty far along in transition before the medical community allows you to get one.