ATM self driving has two issues - the places where it fails in safety are not yet well enough known, and it causes major disruptions for the other cars on the road while turning, parking, or anything that involves interaction / guessing the bahavior of human drivers for something more complex than staying in a lane.
If we would ONLY have self driving cars (no human drivers) and there was some standard they would use to communicate cross company, than self driving would be MUCH faster, not inconvenient, safer and what not else.
As time goes by, there are more and more cars that are being built with the sensors to do self driving, even if they don't have the capability or legal rights.
We will find ourselves in a few years where the majority of cars in certain areas will have the capabilities built in. At that point, some cities will start requiring self driving only, and the software will be built on that assumption. And then suddenly all this effort that Waymo is putting into coexisting with humans will be redundant.