I feel like this only makes sense if you build cities of any size, even when they have 50 people, as if they are ultra-dense. The reality is that public transit takes a certain size city before it reaches critical mass and becomes superior to individual transit. Even where I live (Portland, Oregon) which is considered to have decent public transit, I would have to walk a lot and plan on 2-3 times as long if I wanted to stick with public transit. The density just isn't there yet.

It isn't lack of density, that is a symptom. We don't allows stores, jobs and houses to be within walking distance of each other. As a result you have to drive everywhere. As a result you have to have a car. As a result we need space for lots of cars, as a result things are spread out.

If you had stores and jobs within walking distance of your house you would not need a car. As a result you wouldn't find a car worth having. As a result you wouldn't need all the space dedicated to the car. Also as a result you would take public transportation.

It also hurts that our focus on not allowing change means that even when someone is willing to spend their own money to tear down a smaller house/apartment to replace it with something larger we won't allow it. Thus areas that "want" to grow denser cannot do that. The only option is to grow outwards. That means people need to be farther out, which implies more time in a car, which implies more roads and parking spaces, which in turn means less density is possible.

Note that the above is simplistic. I ignored many other factors. It is a complex problem and no one change can solve it.