[xyzzyz]

> A related and relevant observations why are courier companies not a natural monopoly? If the marginal cost of delivery were high, a courier company with higher volumes would naturally make more profit, and so the market would push in the direction of fewer bigger couriers.

I think you are onto something, that the courier business enjoys huge advantage from economies of scale. However, I think that there is no actual monopoly, because the advantage of higher volume in last-mile delivery probably saturates fast enough that you can take it all at relatively low total levels of volume.

For example, if you have higher volumes, you can optimize courier routes so that they waste less time driving around. However, at some point fixed per-package overhead like parking getting in and out of the truck, walking up to front door, etc become so large that time spent actually moving between deliveries becomes smaller and smaller part of your time, and so optimizing it becomes less and less valuable. Then, the issue is how much volume you need to hit that level, and I think that the answer is "much less than monopoly level".