I think OP's point is (to paraphrase) "why all this when the population is moving into high density cities where this complex infrastructure already exists and presents a superior choice to cars, self-driving or otherwise".

Or from a more global perspective "why all this when the US is the only major market that is likely to continue having a mass suburban population in the long term, and the rest of the world has already urbanized and will continue to do so, already has highly robust mass transit infrastructure, is actively building even more of said infrastructure, and that is rapidly attracting even more population?"

There is a particularly common dream among American urbanists that suburban America will somehow rapidly urbanize - I don't think that's particularly true, but it's certainly true the rest of the world has urbanized, and will continue urbanizing rapidly. So the question is if self-driving personal cars (as opposed to say, commercial cargo vehicles) will largely be an American phenomenon, and if so, doesn't that present fairly modest total addressable market for a company the scale of Apple.