Running a bus to pick up a single person is far less efficient than having that person own a car since the most effective part of a bus is the driver.

Cars scale in smaller increments than most public transit and that is important areas that are not densely populated or during off-peak periods. You can build a nation/culture around public transit, but the path dependencies with the US are pretty deep at this point.

>Car oriented infrastructure simply doesn't scale well as demand increases.

Self-driving cars scale in very different ways than piloted cars. The biggest problems with piloted cars is accidents, congestion and parking. All of these problems fundamentally change with self-driving cars. What Musk is building is self-driving car infrastructure.