I wonder if there's a business in building apps specifically for individual restaurants (chains or even local ones, using cookie-cutter apps) that integrates card processing and such; white label doordash. The business would pay a flat monthly fee for the service and would have to have their own delivery people. Apple Pay et c make the payment side of things painless and prevents people having to re-enter details in each app.

Why isn't this a thing? Is it that few/no restaurants have delivery drivers?

I can't imagine many restaurants benefit that much from the discovery features in UE/DD/etc.