Taxis are expensive because they require a human to drive them. Hence the reason the SDC could change that dynamic. A shared car that does not require an expensive human to drive it.

Another model are shared cars, like dockless scooters and bikes. They are reasonably popular in the Netherlands for example. But they still require quite a bit of planning to ensure the car is available, and they are not always "in front of your door". Also you need to rent it for the entire time that you're away.

Irrespective, SDC will take some time. Like NLP, they work will within a constrained problem domain, but don't really generalise.