You're right that people don't own cars because they are cheaper. But they will, in time, give up on car ownership because autonomous vehicles will be cheaper and better on other dimensions, too. Buses aren't a dedicated, direct ride to anywhere you want to go, so despite being cheaper, they don't stand in for car ownership.
Besides, with enough volume, an autonomous vehicle might pick you up faster from a store's exit faster than you can walk through a parking lot to your car.
I would definitely own my own personal autonomous vehicle. And I think the rest of America would as well. It's this vision of replacing ownership with autonomous taxi fleets that is not going to happen.
They are limited by roads and physics so they'll never have a wait time competitive with a car in the parking lot - and that is the killer.
I do see the allure on the economic side so I understand why this vision is being sold to VCs. But it's going to be just another feature the dealer tries to upsell you on.
Then they wouldn't be any cheaper than a car owned by me. The whole premise is they'd be cheaper from high utilization.
And if not cost what benefit does it have to take a taxi than my own self driving car? I can't leave my things in it. It won't have my radio stations set the way I want. And every trip I'm faced with the guilt of an explicit dollar value for the trip.
Besides, with enough volume, an autonomous vehicle might pick you up faster from a store's exit faster than you can walk through a parking lot to your car.