In that case the interesting question is whether these people who will literally starve to death before losing fat are exceedingly rare metabolic freaks, nothing more than medical curiosities? If their prevalence is in single digits per million they are just a red herring in the discussion of obesity. I suspect that for pretty much any generally accepted and valid health advice there is some exotic medical condition which makes following this advice a horribly wrong thing for that particular individual.

People have literally died of that mistake, so there might be some reason to want to avoid making it-- like tracking what' actually happening to people's bodies when they're trying to lose weight.

Also, disorders tend to exist in a range of intensity, so that's another reason to keep track of the effects of dieting-- even if people whose bodies don't release energy from fat enough to avoid death are very rare, people who who have a lot of difficulty with losing fat shouldn't be assumed to be lying, and may be losing more muscle mass than is good for them.