You'd only need a human while the car is driving. If the human needs to be physically in the car, they couldn't just switch to a different car when this one has

You'd only need a human while the car is driving. If the human needs to be physically in the car, they couldn't just switch to a different car when this one has been parked, and you'd need to organize their own travel when they take a car somewhere remote, or need to fetch it from there. This would still be massively cheaper even if you pay the driver whatever you'd pay them locally for driving in person, simply because of less downtime, e.g. while a truck is being loaded.