I do think this is true. I also think that it's simplified.
I think that this is easy for business travelers, and anybody that's single and / or hasn't started a family yet.
Mobility is more complex as people glob together into families. It's a lot easier to get the car loaded with a group of people and kids going somewhere together, when it's their own car. Some people can go out to the car first to get the herd moving, others will straggle in later. Car seats already in place. You know where the bag of soccer balls gets tossed. All those little details of stuff happening.
Then when you arrive at your destination, there's a bunch of stuff you can leave in your own car because you'll need it for the next stop in the errand run. Are you going to fully unload this robotaxi, carry that stuff around, and then fully load everything back into the next robotaxi? Or are you going to keep the current robotaxi there at the soccer game with the meter running?
My only point is that there are good reasons for having one's own car IN ADDITION TO there being good reasons for some people going carless and relying fully on robotaxi services. In the early days, many people will use robotaxis they way I use Lyft today - a trip or 3 per month because I have a particular transportation need where hauling along my car creates some extra logistics.
- going to the airport (I'd rather not leave my car in airport parking for a week while I'm out of town) and returning from the airport
- taking my car into service (getting back from service; and then returning to service to pickup my car)
Or as
@KarenRei says - because people want them