[insightcheck]

The restaurant could lose out on sales from customers who are dissatisfied with a lack of a physical menu, especially many older people who are not as comfortable using technology or don't even have a data plan.

The restaurant could also lose customers who are tourists, who don't necessarily have a data plan while traveling. While it's a bit more convenient for the restaurant, the convenience comes at the cost of the customer.

Also, the UX for many of the menus is often pretty bad (with diners often asking: "how do I place an order?" "did I place an order or not?" "how do I go back?").