There's usually a security person or two in the store, looking over the self checkouts. I agree that job prevents a lot of people from becoming opportunistic thiefs, but I'm making a distinction between cashiers and security. Today the store needs both.
Pretty sure if a "security person" worked so well, Walmart wouldn't be severely reducing self checkouts at their stores to Walmart Plus members only.
That might be regional, then. I wouldn't say $COUTNRY is exactly a high-trust society, but it's not quite that bad for us over here.
I haven't observed this happening here (Toronto, Canada).