Are they only banned in the cities, or are they banned in the state, which -- even in California, should have rural areas far enough away from cities to be tenable?
It's an interesting conundrum though, because in many cases, the cities could not exist without the things that are being banned in the cities. It's a curious goal of populations to centralize, then ostracize all the things that enabled that centralization
They're probably "not banned" only in the "basically lying" sense that they per rule won't approve you in certain cities and if you do happen to be rural the process is hostile and expensive enough that it's not worth it for the value such a facility would generate. That's how that sort of stuff is in my state.
Everywhere in California that isn't a giant population center is growing food for the rest of the country, or is a mountain where these things can't be built anyway.