The logic is that you give puberty blockers to kids who may or may not become trans adults. If 100% of the kids given puberty blockers go on to transition, that means that you're doing your assessment of "may or may not become trans adults" much too conservatively. So if that's what's happening (and under the unstated assumption that the benefits of puberty blockers outweigh the harms for the "may or may not become trans" group) you should do a less conservative assessment and put more kids on puberty blockers.
That logic is false. What's more, it's known to be false.
Gender dysphoria, which used to be and should still be called gender identity disorder, is not new. We have around 50 years worth of research into the children suffering from this condition. From that research we know (as PP have pointed out), it is the very hormones that puberty blockers are used to suppress that lead to a child reconciling with their body.
In other words, puberty blockers prevent desistance.
That's why watchful waiting has been international best practice in treating children with gender identity disorder (GID).
It adheres to the principle of "first do no harm", as it is well known among the experts that interfering with normal puberty is harmful to children and would therefore needlessly harm the 80% and more of the children diagnosed with gender dysphoria who will eventually manage a successful mind-body-integration.
The real logic is this:
As puberty blockers prevent desistance, putting all children who suffer from gender dysphoria on blockers will increase the number who persist into adulthood.
And this was the best practice logic:
While watchful waiting cannot cure the child whose gender dysphoria will persist into adulthood, it protects the child who will desist because it will not be exposed to the damage that puberty blockers cause.
Puberty blockers bring only one real benefit to the child who persists - a better aesthetic outcome.
And for that we are now putting much larger numbers of all of these children on a medical pathway that closes off their future, damages their brains, renders them sterile, leaves them with heart problems etc etc.