[throwawaysea]

I agree there isn't much real demand for high density housing as much as reluctant demand. What I mean by that, is that no one actually wants to live in high density areas, but they go for it when it gives them access to a desirable location they otherwise can't afford, or if they genuinely want that lifestyle, which I would argue is age-based more than anything. In reality, most people don't like the downsides of high density like crowded public spaces (for example parks), dealing with the habits of bad neighbors (like playing loud music at odd times), increased crime that correlates with urban areas, poor schools guided by populist policies, and so on. If you're young, you might put up with those downsides to get back access to bars or more social networking. But as you age, the value of those things drops significantly for most people.

As for walkability - its utility is vastly overblown in my opinion. Your note about childless adults rings true for me, and the only parents I know who care about walk scores are the ones who are themselves urbanist activists (few in number). Even then, when it came time to purchase a home, walkability was not a decision maker for those couples. To me, that was a signal that even parents who were very anti-car in their political sentiment ultimately didn't put enough of a value on the pro-walk/bike lifestyle to prioritize it when their money was on the line.

I also think it is impractical to not have a car. If you want to live a rich life with access to diverse activities, instead of being boxed into a 15 minute radius or your metro line, then you need a car. Who wants to deny their children the memories of day trips and the thrill of exploration? And if you have a car, then you already have the vehicle you need to live in a more suburban neighborhood, where you can enjoy additional space and safety while still accessing commercial areas in a time efficient manner.