The question isn't so much why vulnerable, confused young people are the cohort most likely to seek a GRC, but why they are still issued in the first place, given the Supreme Court ruling. A piece of paper cannot change your sex, not metaphysically, and certainly not legally, with the GRCs and the Gender Recognition Act creating a self-ID culture that exposes women to men in single-sex spaces and creates unnecessary confusion.
The growth in GRC issuances shows that transgender rights are no fad. Despite what some may say, GRCs are still valid and serve as the gateway to legal recognition of an individual's identity, a pathway that should not be closed. The fact that GRCs still require approval from doctors shows that the process is not easily abused, much to the chagrin of anti-trans fearmongers.