It is like saying that if people need X amount of calories and you decide to put them on a diet by just giving them smaller portions, they will simply eat more

It is like saying that if people need X amount of calories and you decide to put them on a diet by just giving them smaller portions, they will simply eat more portions to hit the calorie level they need. If they smoke for the nicotine, they will smoke until they get the amount they crave. If they smoke because they like something else about it, then they won't. But most people smoke for the nicotine, or they would have some other habit instead.