This is not entirely correct, many places still do accept cash and allow you to order without your phone. It just so happens that most people prefer to order and pay by phone.
We had a sushi restaurant (in Canada) that belonged to Chinese expat that worked with the whole QR code + order + pay on your phone and I did find it pleasant. I would go as far as saying that I prefer it.
It might be cultural, but I can count on a single hand the number of times I went to a restaurant and the interaction with the waiter/waitress improved the overall experience.