At least part of the problem with those kiosks is lack of standardization and/or stability of design. Just when I start to get muscle memory for self-checkout at one store, I go to another and end up looking like an idiot because my usual store lets me put things on the scale and punch in, but another one freaks out, or it doesn't prompt when I expect it too. I had this happen at Whole Amazon a while ago. Pretty embarrassing to be staring at the thing like a deer in the headlights while my mind wandered, wondering what kind of Twilight Zone I was in because the machine was doing nothing when I thought it should do something. Then the assistant pushed the button that needed pushing, and I blushed and muddled through. they probably think I'm stupid is not a pleasant experience, and I'm no stranger to computers. I just don't expect the UI to change that much, or the experience to be so different from place to place.
You would think ATMs, being involved with finance, would be very stable and consistent but I've seen a lot of different UIs and even changes to the UIs rather frequently. There's always that stupid bill selector nonsense. Who wants anything other than $20s? And when you press the bill icon it honks at you. No. You've got to press the danged plus sign??? If you can honk at me, you can make the bill icon do what I expect it to, right? No. They decided to make it honk at me. It took some getting used to. I hit the plus sign now. That means they'll probably change the UI soon--in fact some of them did. They made it harder to get $100 at a time. You can still do it, but more buttons to press. I gave up sometimes and accepted $80.
Anyway, I digress. I've seen a few of these things in fast food places too and it's just like they say--frequently an assistant has to rescue somebody because the interface was counter-intuitive or the thing just plain didn't work.
I don't expect this go get better. Somebody will always think that making a few tweaks to their picture menu will make it better. User-facing sales terminals are probably going to be one long ever-changing Slashdot Beta for a while. It's just human nature that they think changes are needed, when what's really needed is consistency. Ah, but who's consistency? Why, our new company's of course. We've finally got it. We'll solve all the problems created by your N different UIs by having N+1 UIs. Rinse, lather, repeat. Wait, Shampoo used to be under this tab. WHAT HAPPENED?