Only because it's a luxury good that everyone thinks they deserve. Cities that don't expect you to have a car (NY, cities in Europe, most of Seattle) don't really have the same problem, because nobody has a car. And it's not like this doesn't have any precedent. We've mostly car-less cities work before many times.

EDIT: Are you able to reply to my other post now? I think HN has a timer that limits how often you can reply, but I could be wrong.