At least in the USA, no minor is getting GAC in the form of surgery. Not a single person is getting SRS if they’re below the age of 18. There’s like 200 people who’ve gotten top surgery between the age of 16 and 18, but that’s still a minuscule amount. The majority of detransitioners still support gender affirming care.
The most common reason for detransition is lack of available healthcare and social stigma around being openly trans. Around 5% of people who receive GAC regret it, compare that with something like knee surgery that has around a 20% regret rate.
If any person tells you that a teen can just walk into a clinic and get puberty blockers, HRT, or surgery they either haven’t done the bare minimum of research or are lying to you. The only way to get HRT as easy as that is with informed consent, which is only available to adults. If you’re a transgender child you have to go through months or years of therapy before getting prescribed HRT and diagnosed with gender dysphoria, which will only be prescribed to people who are 16 or older in the USA.