It flies in the face of modern food culture, and it's a difficult decision socially. I think this drives a lot of people. That, and they're unable to remove their associations of "how normal people eat" and they feel a lust to consume sugars / complex carbohydrates again. However, the ones that don't start eating more have much better results long-term. You can't get fat again if you don't go back to eating that which got you fat in the first place.