Because we don’t have the technology to actually do that? We don’t even have the technology to replace the guy taking drive through orders. (“You want one Big Mech?”).
This discussion is pointless and premature. There are enormous economic incentives to automate away every job that can be done efficiently though automation. It’s just that our technology is actually very primitive, and that shows when trying to apply it to replacing service workers.
Yeah we do, touchscreen menus (or ATM style pushbutton menus in places with bad weather).
There are factories that assemble frozen mini burgers for supermarkets. There are pizza vending machines out there. So an entire fast food restaurant could be turned into a vending machine with current technology.
(My own guess is that touch screens are still more expensive and buggy than humans, and machine-made food still trades off novelty to be profitable. But I don’t know.)
I'd also be curious to see any user interface studies on these touchscreens. In my limited experiences, they are completely slow and thus an awful experience. They clearly are trying to sell more at every step instead of being useful and efficient for the end user.
You will ultimately order on your phone or a kiosk
Why have people doing crap jobs that are better automated just because they can’t afford to live otherwise? The system is broken, in that we need to better support the folks on the fringes so we can just automate away a lot of mindless, repetitive boring work. The remaining jobs can pay well, and we can stop benchmarking the economy of how many people we put to work regardless of the meaningfulness of what they’re doing.
Why waste a human life flipping burgers or banging away in the mines? Make robots do that, and let’s provide a solution to the displaced, like for instance basic income but totally open to alternatives.