A small town is 10,000-50,000 people. Average home price is $300k. There are around 2,000 towns of 10,000-50,000. That's $18,000,000,000,000 to build some of the small towns in the US to be public transportation friendly. Who gets dragged out of their homes to make room for rebuilding?

And you'll still have to problem that many people don't want to live in crowded towns. Most people that like crowded cities are already living there.