"Stores today are catering to shoppers who perceive self-checkout to be faster than traditional cashiers, even though there's little evidence to support that. But, because customers are doing the work, rather than waiting in line, the experience can feel like it's moving more quickly."
So it's expensive to support and has little traffic. It's not exactly surprising more and more stores, especially high volume ones, let their cash payment processing decline.
The other big speed enhancement is memorization of common PLUs. Seeing bananas and just knowing the code (4011 or 94011 for non organic/ organic respectively) Is a lot faster than trying to navigate through the menus. It's on the label but most people don't seem to realize that.
That said I still think it should be self check out all the way, letting one person run 6 self checkouts at midnight so I don't get caught behind the person buying two shopping carts of misc stuff while I'm just trying to grab an orange juice is miserable.
Replacing 1 cashier/bagger with 10 self-checkout stations with 2 attendants? That'll probably be faster, especially once majority of the shoppers get used to the new system.
Self check out has teething problems mainly because users need get trained on how to do it but once you grok it, you never go back - its simply faster, more efficient experience.