Well, you are not alone. Thousands have felt betrayed. Although positive, their long term effectiveness is very limited. Take for example Dieting. No one can argue about its overall positive impact.
People tend to forget that their body is smarter than they think.
It is a complex self-regulatory system. This explains why so many good people did not lose weight in the long run despite rigorous diets. This also explains why a person with thyrotoxicosis never becomes obese, regardless of how much they eat, and vice versa, a person suffering from hypofunction of the thyroid, can never lose too much weight, unless other disorders are added to compound the clinical picture. The difference nutrition-wise between those two disorders at the opposite ends of the spectrum, is in their Basic Metabolic Rate, which in turn is regulated by complex hormonal and neural control. It becomes obvious, that it is not necessarily how much you eat, but how much you burn, and how effectively your body maintains the balance.