Part of it I think is that Dominos only does delivery, and their product holds up well in delivery. It comes out of the oven very hot, and with an insulated bag, it can sit for a little while and still be good. If you deliver something like Thai food, it doesn't come out as hot, and there are hotter and cooler parts of the food. This doesn't taste great if it takes 20 minutes to get from the kitchen to you.
That, plus the volume, allows Dominos to send out drivers with multiple pizzas. They can calculate an optimal traveling salesman route from the store to all of the customers in the run, and then the driver comes back to the store to do it again. Also, the whole organization is built around the drivers not waiting around. Restaurants will often not have the order when the driver arrives, and they have to mess around with payment, etc for every order.
All of that makes driver productivity much greater and so the delivery cost per order is much less.
That, plus the volume, allows Dominos to send out drivers with multiple pizzas. They can calculate an optimal traveling salesman route from the store to all of the customers in the run, and then the driver comes back to the store to do it again. Also, the whole organization is built around the drivers not waiting around. Restaurants will often not have the order when the driver arrives, and they have to mess around with payment, etc for every order.
All of that makes driver productivity much greater and so the delivery cost per order is much less.