Comment by itake

There are a few problems.

- Real estate: Self-checkout takes minimal floor space. Stores can fit ~10 stations in the area of 2 cashier lanes. Even if you hire more cashiers, there’s no room to add lanes.

- Demand vs. staffing: Checkout demand is dynamic, staffing is static. You can’t instantly add cashiers during a rush, and you don’t want them idle when it’s slow. Self-checkout stations are basically ~free to run.

- Cart size: Trader Joe’s works without self-checkout because their stores are small, carts are tiny, and checkouts max ~20 items. Their cashier lanes are smaller but occupy a bigger share of store space than Walmart or Kroger. In big stores with huge carts, no one wants to be stuck behind a full cart. Once you pick a lane, you’re locked in even if another line moves faster, whereas self checkout lanes are serviced by all machines.

But in the big stores with huge inventories, no one wants to wait behind a person with a huge cart and once you commit to a lane, you're stuck, even if someone else finishes faster.