Basile is correct... dieting is like holding your head underwater... you can do it for a while but eventually your body will do everything in it's power to reach the surface for air... perhaps these set points the obese create are the bodyweight/s their bodies consider as normal... losing such a magnitude of weight e.g. 150lbs, 200lbs, 250lbs + to reverse obesity is a massive undertaking and involves going far far beyond the set points... where is the mental drive in that case?
you are literally fighting your body's process of homeostasis... now the morbidly obese population is not often characterised by their fighting spirit, courage, resiliency, mental and physical fortitude... this is not just the 20-30lbs people lose to get in shape etc. and even that is difficult.