I think there's a few reasons people push for this, not all of them necessarily malicious. If they're already invested in it, say, by having subjected one of their own children to it, they will double down on it, because they don't want to believe they harmed their child. You see it with parents caught up in other kinds of pseudoscience and cult thinking, they have to believe that their healing crystals/avoiding blood transfusions/Jilly juice etc was actually good for their kid and the child's better off now even if horribly maimed or dead, because they can't face the alternative.
As for adult troons, I get that some of them may wish they'd transitioned younger or wish they could have, if it turned out it helped them, but they couldn't have known it would be right for them at that age, and the treatments aren't the same as the ones adults get, they're even worse and we've seen how bad the ones for adults are just in this thread.
Those are the two "well meaning" groups pushing for it. Then there's the doctors and surgeons who are raking it in with all this. People like Gender GP, the sort of people like the Geiers who were pushing Lupron as an "autism cure" before they lost their licenses. Most medical professionals follow strict ethical guidelines but while there's a profit motive in it, you will always get some who try to medicalise anything to sell the cure. They need to be dealt with by the regulators, though some just practise abroad and sell the drugs online.
Then you get the "egg hatchers", the fetishists and the paedos pushing for it. Paedos will try to infiltrate any community, they keep trying to get into various religious groups, schools, medical jobs, anywhere they can access kids, they tried it with the gay rights movement a few times too, but they've been granted much more of a hearing in the trans community, because so much of the campaigning includes removing safeguarding of children.