imo their competition for autonomous vehicles doesn’t come from car companies, but from tech companies.

Amazon has a lucrative incentive to automate its supply chain up to and including last mile delivery. Waymo has proven out the tech and could easily partner with Uber or Lyft for the rider experience and reach.

If you’re FedEx, for example, would you rather buy from Amazon or from Tesla? Who is more likely to be a sane and trustworthy partner?

I don't think that Uber or Lyft are going to invest in self-driving taxis. The capital model is completely different: Uber and Lyft are by design capital light, they own nothing more than the software (1), and someone needs to buy all of these self-driving machines and then someone needs to maintain them, whereas their current model doesn't do that- they can't offer that to any tech partner.

The reason that you don't see more Waymo areas has nothing to do with rider pool or experience, it is because their tech requires pre-mapping everything with LiDAR several times- the advantage is that if you know what is static (because it was in all of that LiDAR mapping) then a simple difference algo can tell you everything that is dynamic in the environment. (Also, they are just starting to hit cities with significant precipitation- SFO, LA, ATX, PHX are all pretty dry cities, they are going into ATL, MIA, DC, DEN, etc.)

1: With a lot of suspicion that much of their profit comes from drivers not understanding depreciation of their vehicles, something that the accountants who work for Uber and Lyft will understand very very well.