Pizza delivery is generally handled by each individual restaurant with some dedicated employees, so it's a pretty different model than something like Uber Eats. Pizza is also fast, cheap, and simple, so that helps to drive down costs. It's also generally a complete meal for at least two people, if not a whole group, and so the delivery cost gets split across more people.
I get the comparison, but I don't think they're really as analogous as they seem. One is a pizza place hiring a delivery person or two to drive some pizza around; the other is a large tech company settled with debt and inventor obligations paying very expensive engineers to manage incredibly complicated logistics networks and deal with tens of thousands of distinct parties.
This is really kinda my point. Why is pizza delivery so much cheaper? Because it doesn't have to deal with all these extra costs that a massive delivery network like Uber inherently has to manage. I imagine we'll eventually hit some kind of equilibrium where a lot of restaurants that can manage it have their own in-house delivery people, while the large networks will have to dramatically downsize or die.