You're not wrong, but it's not just the UI on the kiosk, it's the whole checkout process. A trained cashier on a real checkout line is much faster because the machine isn't nerfed and trying to hold their hand while preventing them from stealing. The real problem is the stores are trying to shift the labor onto the customer but the customer isn't getting much benefit for the effort nor has any motivation to be particularly honest in light of having this chore thrown in their lap.

I don't think they can redesign the UI to overcome that. It's not really a UI problem, it's a conflict of interests problem and they're not going to solve that unless they completely redesign the checkout process. The little Amazon convenience stores that know what you have as you shop seem like a better approach, but I'm guessing they're not all they're cracked up to be since they haven't seemed to catch on that much.