There are so many cities (I'd say it's the majority in the world), with mixed use zoning which work wonderfully. Lower floors are offices or businesses and upper floors are apartments. Why is this so difficult?
part of the reason this is so bad in the USA is indeed what OP named, the concept of 'legibility', as explained in 'seeing like a state'.
In the case of the USA, though, another 'lens' on the legibility is that overall the people making the laws were neurotically concerned with keeping black people away from white people and enforcing segregation.
'separating uses' was a good way to also 'separate users', and a little barely-that-creative law-writing lets someone keep black people quite removed from the white people.
I found a document from 1922 that is upstream of all american zoning codes - it's what got ratified in Euclid v. Ambler circa 1926.
It's explicit goal was:
"To maintain harmonious relations between the races, care has been given to ensure adequate separation between the two, with room to grow without encroaching on the other"
"The ordinary two or three story store and dwelling building is not a desirable type of construction from a public stand point. The regulations as applied will tend to reduce the number of flats that would otherwise be located over stores."
So - there it is. The goal of American zoning was, in part, to eliminate 'the ordinary two or three story store and dwelling building'.
"Unlivable" isn't normally used in the literal sense. A nasty, unheated, rat-infested apartment, for instance, can be said to be "unlivable", though it really is possible to live there if you're desperate enough.
I swear, it's impossible to please people. People are complaining that mixed use zoning on Taraval street in SF is wasting space because the street-level floors are wasted and they should be converted into apartments (many business have shuttered and ground floors remain empty in some mixed use buildings).
It would be terrible loss to convert those business spaces into residential. One or two could be changed, as retail needs change over time, but removing possible retail and third space from near people's homes means less walkable neighborhoods.
Where I live, we have short term reuse laws that allow retail spaces to be used for residential, social, or other uses on a fixed basis. Typically a few years. The idea being to review the reassignment when the local needs change.
We get a lot of kindergartens that use these spaces, but also pharmacies, social clubs, and offices. Easy to move in and out.
Why do the ground floors have to be designated by the government as retail or residential? Is it impossible to say it can be either, as long as the requirements for whichever one (e.g. ventilation, fire safety) are met?
People are complaining about mixed use zoning? Geez, there's already a fair amount of mixed use along Taraval anyways. A real common narrative was that the folks in the Parkside don't want to turn their neighborhood into Manhattan (lol). The other one was the staunchly anti-transit narrative pushed by the guy that owns Great Wall Hardware on 28th, Albert Chow. That guy publicly fought tooth and nail against putting boarding islands up along Taraval (the Examiner got some choice quotes).
Anyways, it's been a hot moment since I've paid attention, but years ago the guy that owned the hardware store on 44th Ave tried to convert into a mixed use building. I don't remember a lot of objection, but then the real estate market tanked and he went out of business. The apartments got built at least…
