Manufactured homes are a thing. You can literally buy one for 100k-300k
Most homes in my area have two (3 with basement), traditional single story ranch doesn’t make good use of the limited land. So if multiple floors aren’t available they’re not an option for a great many homes.
It’s kind of amazing we’ve perfected the subdivision. Building and rebuilding the same 3 floor plans a hundred times over by hand. It’s automated in a way and yet not automated at all.
Once you get into this territory, at least in the US, it makes more economical sense to have a builder create a 2/3 story home.