Many places do. It was very much the norm as cities were expanding rapidly in the 20th century. Something like 75+% of land in major metropolitan areas in North America are zoned for single-family housing only[1]. And of course that's not evenly distributed between cities, and much of the remaining 25% is still zoned as exclusively residential or commercial.

[1] https://www.nytimes.com/interactive/2019/06/18/upshot/cities...