The barrier to expansion is that suburban sprawly cities have been designed around cars, shared transportation under-developed, and wealthy folks are scared of being too close to less wealthy folks, who they think will try and steal their stuff or cough on them.

Relatively rich, conservative suburban folks are going to make choices to disadvantage less-wealthy people (like those that are historically going to need public transport and can't afford a car, or a second at least). It's easy to raise a group of people's outrage through scare rhetoric; that's why we the US has it's current administration. It's also not a good reason to just say "oh well buy more cars".