You don't walk into book stores to ask employees for the book you want. You browse, look, read, and finally select a book. No interaction with humans required. (There's human interaction at the point-of-sale, but you still don't have to speak to checkout.) Of course, if they didn't have the book you wanted, you might have to speak to a human to get it ordered ... if they didn't have computer kiosks for you to use instead.

Moving this type of sale onto the internet was not a change. Moving the food service industry, where human interaction is expected, into an environment without human interaction goes against people's expectations and habits. Is such a change technically feasible? Yes. Is it practical? Yes. Profitable? Sure, if you can change people's expectations.

I'm not saying it's a bad idea. I don't even think it'll be a difficult change. I personally would prefer it. But the first chain of restaurants to offer automated food service (and I do believe it'll need to be a chain) has many psychological barriers to overcome, in its investors and its customers.