Jazz's sudden influx of massive weight is a further demonstration that he still has not developed enough mentally or emotionally to be able to process consequences and self-control, both things that would be MANDATORY when considering full-fledged transition. Even though his brain, had it not been on hormones, still has another decade to go in terms of development, by the time you become a young adult, you should have reached a level of understanding in how to properly diet and exercise.
Most people who binge to the level we know Jazz does either a.) Are suffering some kind of trauma/mental disorder, b.) Have unhealthy coping skills, c.) Have delayed maturity. And so on. All of which Jazz could be lumped into easily. Realistically, the fact that he's still ballooning while being watched like a hawk under the eye of Mommy Dearest should say more about Jazz's lack of development than anything else.
A child doesn't give a shit if they balloon. An adult is proactive in putting an end to such things. But in every picture we see of Jazz, he looks heavier than ever. His body is literally evolving more and more negatively before our eyes and I don't think his stunted mind can even realize the consequences of this. On the show, whenever someone points out Jazz's weight, he mostly just brushes it off or shrugs and says that he likes food. You know, the way a kid would. An adult would either get defensive or would spend time worrying about it. But not Jazz!