But they're not robots - they've just outsourced the checkout job to the customer and made it so they require minimal training. Technology has made this easier, but it's not robotics.
That being said, I think the robots that have taken peoples jobs are generally in warehouses and manufacturing and hidden away from the public eye. Think Amazon fulfilment centres, or auto manufacturers. There are a lot of robotics at play there replacing a lot of people.
Self checkout is logic automation, making the checkout job easy enough that customer can be trusted to do it.
Checkout used to have two jobs: a checker and a customer standing around waiting. Self-checkout merged those two jobs into one.