Also, it varies from city to city (and within cities). Although most of the 20-35 crowd probably would prefer a denser city, old people prefer owning homes with lawns, so they wouldn't even want to live in that kind of place to begin with.

It's very difficult to find a place like our house in Italy in the US: we could walk to schools, grocery stories, pastry shops, our doctor, cafes, pizza place, a few barbers and a tram stop to go downtown.

And that's in a suburb of a mid-size city (about 300K).

Now, it’s not perfect: the T breaks down all the time due to criminal underinvestment, my bike commute is noticeably faster than driving through the traffic, the mass transit schedule is such that any route with multiple transfers is insane.

But I’m going to guess that the Italian and Dutch versions of this aren’t perfect either; it’s a matter of deciding which flaws to live with.

Even dense US towns are zoned against density. Somerville, Massachusetts had a rude awakening 5 years ago when they discovered the entire city is in violation of the zoning code. Every single home is out of compliance for one reason or another.

That's fine, but why do old people need it legally mandated that everyone has to do that?

What's the justification for that?

I don't really agree that developers are particularly responsive to the market in this regard, either. Or rather, they make quite a lot more profit from two 6K lot houses than they do from a more expensive house on a 12K lot. Builders always, always want to go for smaller lots unless they're selling super-premium houses of at least $1M (for context, the average house price here is probably right around $350-400K right now).

Your example does not show that developers are not responsive to the market. The fact that developers can make more profit on two 6K lot houses than they do from a more expensive house on a 12K lot simply means that there is more economic value in satisfying two peoples' desires for a 6K lot house than in satisfying one person's desire for a 12K lot house.

If you eliminated the minimum lot size, people who want big lots would have to pay a lot more for them to make it worth developers' while, and that makes total sense! One person buying a house with a 12K lot pushes out two people who might be perfectly happy with a 6K lot. They should pay more.

(It may be true that there literally are no municipalities in the US with zoning codes that allow dense neighborhoods, but I would be highly surprised.)

In most parts of the US, you can no longer build those dense, walkable, mixed use neighborhoods that make it convenient to live without a car.

There was a study a Few years about about which cities and suburbs could be built under their current zoning laws. I remember it showing that Somerville—a dense collection of 3-decker houses near Boston—was completely impossible to build under its current laws. I don’t have the link handy, but happy googling.

And that's in cities. Extend it out to podunk and they have to be subsidized, even when they don't know that's what's happening. And it's getting bad enough many counties in the U.S. have started to revert paved county roads back into gravel because they simply don't have the money to maintain the paving. They're worse full of pot holes than gravel. And the locals don't want to pay their fair share which might mean a dozen families sharing 50 miles of road - it's the exact opposite of economies of scale. Their incomes obviously have not kept up with the cost of even maintaining local roads... but there's no market force that's really correcting for this either.