Some people will definitely buy more. One look at global obesity rates shows that people don't buy less food just because they don't need to eat that much. He/she didn't say everyone would buy more, just some percentage. You're obviously not part of that percentage, which is great. But it doesn't have to be many who do to make the effort of rearranging worth it for stores. 1% of people buying more means millions of dollars for a big box chain that does hundreds of millions in sales every year.

But ultimately it's a combination of things. Some buy more. Some buy different brands they don't usually buy. Maybe those brands have a few more in the package than other brands and people unwittingly buy more. Maybe they try an entirely new product line they've never tried and it becomes a new normal thing.

As an adult it makes me mad mostly because I know I'm being played and being made intentionally less efficient but I have to deal with it anyway because I don't really have a choice.