Zoning calls them "single family homes" but it doesn't call it "nuclear family homes" or anything like that. Single family homes are more about American individualism[0] and not wanting to share anything if you don't absolutely have to. That's why, outside of at most a couple aberrations like NYC (where multi-generational families live in condos all together or else fragmented around a neighborhood but still within walking/subway distance of each other), we have a fetishized (less so in recent decades) car and road culture and insane density-averse zoning policy instead of shared infrastructure and dense, affordable housing.
[0] or at least, as idolized by those who made the zoning rules so long ago. so... go change them! Get into local office. Get into state office. I'm no iconoclast, but there are definitely some long-standing norms and "traditions" in our society that could stand to go.