Most of the world doesn't have decent public transport because most of the world is -- rapidly -- developing. In the same vein, most of the world doesn't have decent internet access (I'm not saying the two are very similar in other regards). It's a bit early to say whether the developing world will end up with decent public transport. They're certainly trying with some success. They're also acquiring cars at an astounding rate, they're going to have to do major infrastructure works at enormous cost either way, hopefully they're smart about it.

As for the rest; living without a car doesn't require anybody to live in an arcology or in a "hyperdense" urban area. Most of the world (ie >50%) already lives in an urban area. There are lots of medium-sized or even big cities that aren't hyperdense by any sensible definition of that word. I don't think most people consider it hell on earth.