It is in their best interest because puberty blockers are harmless and this gives the child more time to figure out what they want. If they want to go ahead with transitioning they can take the appropriate hormones when they're ready. If they change their mind and don't want to transition anymore no harm is done. Maybe you were under the impression that puberty blockers have permanent effects?

Puberty blockers just give children extra time to figure out what they want, and it sounds like you agree that's a good thing.