More likely that they have multiple reasons to be unhappy, and transitioning was insufficient to solve it. They may have been misdiagnosed in the first place, or were correctly diagnosed but attribute their remaining difficulties to the transition. Or they found difficulties being accepted in their new gender.

This is a problem throughout medicine: some treatments work, some don't, and we don't always know why. The vast majority of people who transition are helped by it, in part because of the extensive screening. Despite the hysterical tone of books like this, it's not something people do on a whim.

That doesn't mean it will help everybody, and those are unfortunate. But it's irrational to withhold a treatment that helps most patients because of a tiny number of negative outcomes -- especially when those outcomes are artificially given outsized influence by ideologues who have entirely un-medical reasons for opposing them.