My neighbor works at a Walmart in the US and observes the following: They won't usually have more than 2 or 3 cashiers signed in at once. The cashiers are either elderly people who can't scan super fast or young people who don't care. So most people go to the self checkout unless they have a cart brimming full of stuff, and even then she sees more than a few go through the self checkout anyway.

Is this Walmart being cheap? Kinda, but I think the recent surge in living costs has made being a Walmart cashier an unattractive job. I think they have trouble keeping and retaining people who want to do the job and do it well. $15/hr. is nothing now, and the young people who are cashiers know that.