[Melusine]

It's because a lot of people are lazy - they want to lose weight, but they don't want to do anything about it. So they just lie to themselves and think, well Product X guarantees that all I need to do is take this pill thrice daily and then I can eat anything I want and still lose weight. Which of course is bollocks, but 'it sounds so great'...
That, and the fact that it's simply very difficult to get out of the downward spiral of bad eating habits... People will try anything that promises to help with that. Once your stomach is used to large quantities of food, dieting will leave you constantly hungry...