I'm trans and I support therapy before HRT, but I disagree with the sentiment that it's because of possibilities of regret. I believe that gender-focused therapy helps one prepare for the changes and challenges they will endure on HRT - it's a big step, afterall. Approaching medical transition with strong mental health is essential to wellbeing while undergoing difficult and impactful changes.

For context, when I started on HRT in the early 2010s it was normal to be required to have a panel interview with your therapist, another mental health professional, and a medical doctor (with whom you had had a physical exam and blood tests) to present your case and ensure that HRT was the best treatment option before starting. It was a rite of passage for trans people who pursued HRT. I'm glad that things have gotten easier now, but at the time it helped me feel certain that I was ready and fully prepared.