You're on the hook for more than a supervisor. Depreciation, financing, or lease payments on the robots is a big one.

And what do the robots do? Wheel the food to the table, where the customers then need to reach for the plates and pass them around? Not a great experience. Or actually set the plate in front of each diner, without dumping it, like a human waiter does? Much more sophisticated and expensive robot.

Indeed; it seems like the market niche for this would be relatively small.

It's not fast food, because customers pick up their own food from the counter there. Ditto with fast casual.

Fine dining restaurants would see huge drops in business if they tried to replace human wait staff with robots. (Unless they're already doing some kind of futuristic theming.)

So you're targeting low-end table-service restaurants...to replace their below-minimum-wage wait staff (remember, tipped minimum wage is something like $2.30 federally) with robots that don't get tips, do require a hefty up-front investment and nontrivial maintenance costs, probably a subscription with the company that sells them, and are likely to have a lot of problems especially for the early adopters—things like dropping meals, crashing into tables, crashing into customers, running over toes, purses, and small children...

This really seems like it's something that's going to work for a few gimmicks, but not in any widespread manner within the foreseeable future.