I've highlighted the two main issues you are currently experiencing.
They're being conservative with their rollout mostly because of civic issues. Most places do not have a legal framework for "what if your autonomous vehicle hits someone?" yet. Even if Waymos never were at fault for a collision with a person, you can always have cases like the one in Georgia back in October where a bicyclist wasn't looking where they were going and rammed into one. The shaky legal ground is a pretty big impediment right now, and that's in the US where we have much laxer laws about corporations killing people.
Then, there will be concerns about the scaling costs. If it makes economical sense only in densely populated zones, what's the point? I mean, yes, it will be yet another business that works only in cities in that case, but that will not then make it universal as cars are.