It's (obviously) a function of store design, staffing, and demand. FWIW, in Basel (Switzerland) there are often large queues at the weekends/late evenings in t

It's (obviously) a function of store design, staffing, and demand. FWIW, in Basel (Switzerland) there are often large queues at the weekends/late evenings in the (only) two supermarkets which are open, despite self-checkouts. They are relatively small stores near the station, and serve very high demand driven by Switzerland's opening-time restrictions.