My colleague lives in a European city which has undergone a building boom, and it was surprising to me how density doesn't just mean more people per area, but also more area per person. A very spacious apartment is much more affordable there than in any major US city, and more people therefore get more space to themselves. It's kind of amazing how much more livable that arrangement is.
Spacious apartments aren't nearly as possible in the US because of various deficiencies in our building codes, one major one being that single stair buildings aren't allowed, which means apartment buildings have to be built like hotels.
US building codes aren't national but local. The local may point to one of the national association standards like the IBC or NFPA standards and such. But they then add/remove from those standards as they like.
This is a problem people need to take up on local level.
They still have enough other changes that we can't build something like a cavernous old NYC apartment, though I don't remember the other issues. I think it might be related to nobody wanting to build condos because they'll get sued for it.
