I agree with ChristinS. Most are gimmicks using the basics for weight loss and repackaging them. The formula for weight loss, while remembering weight loss is not necessarily fat loss, has been the same since who knows when. To loose one pound of body fat the body has to burn 3,500 calories. How one gets there is what is packaged by weight loss programs.
Adding to this seeking 'why' success is lacking could be said the lack of fortitude. The parameters are infinite, yet simply the fortitude needed to overcome discomfort is lost somehow and someway.
However, that does not address maintaining a desired weight. Again, as ChristinS shares it is calorie intake and exercise to meet the minimum needed calorie balance for weight and hopefully body fat maintenance.