Because I like having my personal car, where I hop in and the seats, temperature and music are set to what I like, there's no weird smells and I have privacy and comfort. Besides, I think that about 60% of taxi drivers should never be in charge of any motor vehicle and are completely incompetent at driving, I don't feel safe at all. But that's beside the point and will be fixed by autonomous cars. But being in a vehicle shared by others will not, and I have no interest in doing that, just like I have no interest in taking a bus.
But yes, I have just done the calculation and it would in fact be cheaper for me to uber to work than to own my car. Yet I still prefer to have my own car that yes, does absolutely nothing for 95% of the month.
I still think fully autonomous cars would let you have your cake and eat it too. Maybe you don't want smelly passengers in your car or to have it unavailable at certain times of the day or week. That could be done. Maybe the rental car is available to you during the day but moonlights as a driver for Amazon packages?
It could all be spelled out in a service level agreement.
