I'd venture to say that around half the people who own a car today would be a lot better off financially if they didn't need one. Car ownership is very expensive and a huge hassle. And so many people are one major car repair away from financial ruin.I'm not sure that vehicle ownership will decrease on average once RT is a reality. I think people will have dedicated personal vehicles for themselves and a fleet of vehicles to work on the RT network so long as it remains a profitable endeavor.
If robotaxi is a workable, lower cost alternative then most will opt for a nicer place to live instead of owning cars.