She just wants to be loved and admired constantly (which, needless to say is not a realistic or healthy life goal for anyone) but in order to do that she needs to be a weight loss success, a youtube inspiration... or at the very least, to appear as if she is "trying."
I don't think I've been following Amber for as long as you have, but I too remember when this sub-forum was just a thread. Unlike many here, Kiwi Farms introduced me to Amber.
I came to the same conclusion as you by noticing the titles she used to give to her videos and her behaviour in videos after a new weight loss "journey" would begin.
Amber is no genius, but she has an uncanny ability to manipulate YT to her benefit. Before she reached 500lb there were plenty of videos with titles like "what a 500lb girl eats", "fat girl exercises" and variations of 500lbs/fat girl does
insert activity here.
Amber has been selling herself as the circus' fat lady for years now. If she lost the weight, she would lose her "job". Besides, up until recently (and Amber admits that in a video made a few days/weeks ago), she was the fat girl with the pretty face/hair. If she lost the weight she would be just another girl. All the "specialness" would be gone.
As for her behaviour every time she announces a new diet, I noticed that as soon as the few videos showing how excited she is to finally lose weight are done, Amber gets very "defensive" and easily butthurt and slows/stops making videos/talking about her "journey".
I suspect the reason she becomes so "defensive" and "butthurt" is because she isn't really doing anything and is afraid of her lies coming to light, so she takes a break from the "negativity".
IMO she doesn't have to be a weight loss success story, all she has to do is continue to be the freak show. Amber wheels people in with the promise of a shared journey, but she knows that many of the people who stick to her are going to eventually use her videos to feel better about themselves. She also knows that the only people remaining for the long run are the haydurz, and that she will be mocked.
Her ego demands she stops making videos/sharing her life, but her greed forces her to come back. So far the greed is winning, but it's breaking her in the process.