This is generally not possible at twice the cost. The robots generally suck and break down a lot. Now you've replaced a bunch of low-skilled, interchangeable staff who work like dogs with a fleet of mechanics and an engineering department.
Half of the McDonald's automated kiosks I see are broken - and it's usually the store's entire system down, for weeks or months on end. I went to Home Depot today to grab some WD-40, and when I went to do the self-checkout, each of the four stations had a clerk helping the customer "self" checkout. To circle back to McDonald's - it's always been a joke how difficult some fast food clerks find their POS systems - where does this fantasy come from that customers are going to be better at it?
When it is possible to automate a job away, it is desirable. It's good that raising labor costs drives technology development. The better technology we have, the more comfortable we can all be, and the less we have to work as a species.