I think the key issue is that "owning" a car comes with a lot of expectations on behalf of existing customers. People are going to say that if they own it they

I think the key issue is that "owning" a car comes with a lot of expectations on behalf of existing customers. People are going to say that if they own it they should be able to mod it as they please, is that actually practical with a self driving car? What if they mod it in some way that makes it dangerous? Who's liable? There's a whole host of issues like this and most of them go away completely if you can't buy a self driving car but you can rent it per ride. Plus, if they do run it as a taxi service I think they can iterate everything from hardware, software and even infrastructure that supports it much faster than if they're selling it. I think google will be content to run a taxi service and let others sell self driving cars if and when they catch up because honestly it's a better business than outright selling cars.