[Falkon1313]

The uber/lyft/limo large cars vs standard cabs/cars are usually used for a trip when there are more passengers or cargo. With private cars, the larger ones are bought when there might ever be a trip with more passengers or cargo, even if 99% of the time they just have a single occupant.

Also normal cars spend most of their time parked. Driverless taxis wouldn't need to.