Australia

It might be a bit more difficult for them than for Woolies and Coles, sure. But Australia is unique in how strong Colesworths are, and yet in other countries, as demonstrated in the video linked above, stores are able to have scan & go tech.

Granted, there are a whole bunch of other factors in the Australian market that make it way worse than it needs to be, like our restrictive zoning practices that promote driving to big supermarkets rather than stopping off at your local small store on the ride home or walk back from the train/tram/bus stop. But the bottom line in terms of their inability to provide customer conveniences is that if stores in a country that is both less centralised and lower population can do it, there's really no excuse here. Pubs and clubs have gotten on board with it via the prevalence of QR codes to order food, despite menus being unique to every place. Maccas manages to have a pretty damn good app experience despite prices and menus varying somewhat between stores and being largely franchise-owned.

They don't need to spend millions developing this for themselves. A quick search turns up numerous different while-label services that can do this for you. I don't know exactly how much they cost or how hard they are to integrate, but I know I would be way more likely to go to somewhere other than Colesworth if the experience didn't suck arse. Last time I went to my local local store (there's also an IGA pretty nearby that I do visit from time-to-time, but this was a fully independent local grocer) they refused to check me out at all because I didn't have cash, and they only accepted cash for small purchases.

Your last paragraph is a good point, and is yet another reason that the government should structure its laws and enforcement to help promote these smaller businesses rather than CostlesWorthdi. But I think it's unlikely to sway very many shoppers.