Pizza deliveries are all basically that last-mile, you're not normally ordering a pizza from another city/country.

That means the company has lots of individual restaurants with their own delivery operations (guys on bikes) who handle that last mile on an individual basis, or maybe doing a couple of pizzas at a time.

If you've ordered a pizza, then you're also pretty much guaranteed to be at home. There's not much point leaving a note saying your pizza was taken back to the depot or left with your neighbour!