A car, as currently used, is not just a transport mechanism. It's also a storage mechanism. (Umbrella, sunglasses, kids' car seats, emergency diapers, emergency cash, emergency feminine products, OTC meds (ibuprofen, antacids, etc), a reasonably secure place to keep my backpack if I don't want to carry it, mints/candy, etc.)

Automating a taxi service doesn't 100% replace the utility of a personal car.