> Because if people went to all-pizzas.com for their pizza need then each restaurant and chain would depend on them not to screw them up

This is precisely what makes food delivery ordering services (GrubHub, UberEats, Deliveroo, etc.) so challenging to operate and maintain. Practically every restaurant accepts orders in a different way, and maintaining custom mechanisms for each one is costly. Restaurant front-of-house technology companies like Toast are helping make them operate alike, but adoption is slow and there are many, many restaurants to tackle.