Wait what? What's preventing merchants from doing this now? Why even fill the pizza boxes? I must be missing something...
As for why fill the boxes, technically DoorDash would be the store's customer, so if you didn't give them what was ordered they could press the issue. It'd be hard to police, as the person making the DoorDash order wouldn't complain, but it adds a way things could fail.
Plus, the post said dough at that scale is practically free.
If I was driver and the pizzeria handed me empty boxes I’d refuse to deliver and I’d call DoorDash. Ain’t no way I’d take empty boxes to a customer and then have the customer potentially accuse me of removing all of the food they paid for.