For most, dieting is to maintain the status quo. Overweight or obese people drink and eat diet beverages/foods, or conform to some self-imposed diet, to maintain their current health. They know they can't give 100% into their desires, or they could have dire consequences (hospitalization, death), but they are not determined enough to take the actual steps to losing weight (significant diet change, routine exercise).
I see this everywhere. Family, friends, etc. They all say they're dieting, but year after year they are as out of shape as always. They are happy and content with themselves, because dieting to them does not mean "get fit like those gym guys on T.V."