You're right - none of them ever said anything about how to maintain the weight loss.

That's because they knew they were not sustainable diets to begin with, that as soon as you gave up on trying to stick to the diet (or more rarely actually lost the amount of weight you wanted to lose), you'd go off the diet due to vacation, holidays, or life in general, and gain it all back... just in time to buy the next issue of the magazine to get the ALL NEW PERFECT WEIGHT LOSS DIET PLAN.