Yeah there are confounding factors at play here, such as there being many automated checkouts but only one with a person.
> staff ... "training" less-savvy customers to use them.
Training the customers is one of the things I find most depressing. From the supermarket's perspective, customers have apparently accepted that they must do unpaid work that used to be done by paid staff. Scanning items, typing in product codes when the scanner doesn't work, looking up loose goods in a catalogue and weighing them, responding to beeps and prompts, etc. And even better, watching advertising. Sure, these are all 'first world problems', but societies should be improving their citizens' lives rather than whittling away their autonomy. It might be just a papercut, but it's death by a billion papercuts.
> I'd much rather minimize my interactions with strangers while shopping.
Social isolation is a major and growing problem in western societies (see my other comment). People choose the path of least resistance even if it's long-term suboptimal, and minimising interactions with strangers seems like an unfortunate choice. Obviously, I'm making a bunch of assumptions that might not be fair, and you have my sympathies if your neighbourhood is full of arseholes :)