Possibly because of the tendency to view certain groups as above criticism? This used to be the case with Catholic priests and that allowed cover for some who were abusing children. Bad actors will always choose such cover if they are able to do so. This doesn't mean that they would be a large percentage of the group, of course.
This may be linked to connecting unrelated issues under one wide Stonewall umbrella, as if all of them had the exactly same motivations and causes behind them, and then making discussing the possibility that this, perhaps, is not the case forbidden. The #nodebate rule.
So we cannot ask if, say, a young girl and a middle-aged married man might, actually, be transitioning for quite different reasons.