It's a very simple, appealing story, that can be sustained in the face of evidence that the original theoretical model does not hold up.
It might be sufficient to give them something they think they can sell, and something that various political interests think they can get away with buying. But most people need a story - they want to know who, what, where, when, why, and how. If they are merely told that something happens, but not why or how, they can't visualize it and don't trust the story.
This is why, having decided the cure must be CBT/GET, the quacks have filled in the "how" with theories of deconditioning and fear avoidance. This gives some other therapists something to grasp onto, that they can understand. Then they can feel confident enough to essentially torture their patient as instructed.
If there's no "how" or "why" for CBT/GET, we get into the realm of more blatant quackery. Then we might as well substitute CBT/GET for homeopathy, crystals, or placebo - it doesn't have to make sense, so it's all the same. We just need a few people to say they feel better. But most therapists are not going to go along with it without an explanation. They need at least a veneer of an explanation, even if it's baseless psychobabble which has never been more than a vague hypothesis.
This is why motive is an important part of every criminal case, even though it's almost never a required element of criminal laws. People need a story that they can make sense of. The psychobabblers will shoot themselves in the foot if they omit one, and they probably know that. But if they can't use deconditioning or fear avoidance, they have to invent a new story for presenting CBT/GET as the cure.
I think this is why central sensitization has been gaining popularity, as deconditioning has been disproven and fear avoidance falls flat, especially with patients who know damned well they aren't afraid or catastrophizing. It's even more vague than fear avoidance, it allows them to smile while telling patients of course they aren't deliberately causing their own symptoms ... but CBT/GET is still the cure for fixing that tricky brain.
Naturally this still relies upon ignoring nearly all biomedical research into ME/CFS, but they've been doing that for decades. And I think that forcing that biomedical research to be systematically acknowledged is the only thing that will force a change. The quacks will always invent a new pseudoscientific hypothesis as the previous ones are knocked down. The only thing that will stop them is a lack of funding, a lack of support from their institutions, and condemnation from their peers when they try to do it again.