I have seen supermarket chains do away with automated checkout (Jewel which parent company is Albertsons) systems because they increased loss factors.
Cut staff numbers without having to pay for increased security! That's just good business sense.
They don't pay for the police?
Scanning while you shop, however, doesn't really seem to work. Tesco tried that and basically stopped it again. You either need to check really often (high staff costs) or will have losses.
Carrefour does that in France, and it works like a charm (I've used that for years when I used to live there). They run semi-random manual inspection of your grocery bag at checkout (happened like once every 1-2 months).