There's tradeoffs everywhere. Sure, if your car is out giving someone else a ride, it can't give you one either. But most of the time when you get in your car, you know ahead of time that you're going to do that, so it's pretty easy to tell your car to become available when you need it. And the benefits to owning it include having it available exactly when you need it (instead of having to call a car and stand around waiting for it to come pick you up), having it be able to sit around on standby for if you don't know if you're going to need it or not, or personalization of your car, etc. Similarly, if you're regularly driving longer distances than just hopping around San Francisco, it's probably more cost-effective to own a car than to use Uber. And once you go outside of major metropolitan areas there's a lot less coverage by ridesharing services, and it's reasonable to expect there to still be low coverage by Uber-owned autonomous vehicles.