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.
I know. Nobody else does though.
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.
Single family homes are literally the least efficient use of space. They are the reason there isn't enough space for parks in the first place.
I agree that you might more schools, but given how much lower the birthrate is, the existing facilities are likely ok.