It's NIMBYism and zoning. People individually may want/demand apartments or townhomes or duplexes, but for various reasons it's common to outlaw all those thing

It's NIMBYism and zoning. People individually may want/demand apartments or townhomes or duplexes, but for various reasons it's common to outlaw all those things via local zoning regulations on most of the residential land in a city or town. Even in major cities, this is usually true (though of course there's some exceptions), that most of the land is reserved exclusively for detached single family homes on large lots. In contrast, some countries like Germany or Japan don't have that type of zoning anywhere in the entire country. Of course, they still have many single family homes, you're just not required to live in one if you want to live on a particular street. I don't want to get into the justifications for mandatory SFH zoning, but the results are pretty clear: it makes walking, biking and transit worse (and thus makes people less healthy and fatter); it results in economic segregation, as a working class family can't move to an affluent area by moving into a smaller home there, because smaller homes there are illegal; lastly, it means higher housing costs, because you can't put as much housing in a given area to meet demand (this also tends to increase commute times, as people go further out from the job center area to reduce costs).