It's interesting that overall spending doesn't decrease that much in the end, although shifting from snacks to fruit is the kind of change health advocates have always wanted?
Deserts are visible - obviously a pack of Little Debbies has no nutritional value and is purely excess calories - but what fraction of your total calories are coming from deserts? The real issue is excess calories in your regular food consumption, such as large portions. Indeed, if your meals were filling you, you probably wouldn't even be snacking to begin with. When comparing things like bread and butter, the ultra processed versions are much cheaper. In absolute calorie terms they have lower sticker prices, but they also genuinely appear to be better value: you can get significantly more volume of food, and it will last substantially longer meaning you can buy in bulk, reduce the amount of time you spend grocery shopping, and spread purchases out to better align with when money is available. More often than not they also require less time and effort to prepare good tasting meals.