The problem is that the vast majority of food stamp users aren’t bargain seekers. To them its free money so why bother maximizing it.
If these are people who have enough excess funds that the foodstamps are superfluous... well they shouldn’t be getting them. They should be for those who would be catastrophically without food if it weren’t for the stamps.
Certain items (e.g., cigarettes, alcohol, etc.) are supposed to be off limits for food stamps, but I see them used all the time. Checkout people either don’t care or are intimidated and don’t push the point. One time when I saw it happen in the checkout in front of me, I told the lady (?) that my money paid for those food stamps and that I’d appreciate it if she bought food with them. She told me to “F@## off”. I called the manager over and she was not allowed to check out. She was more than a little miffed.