I'm pretty sure no new mobile home parks have been approved in this area for many, many years and I think that's true for many areas in California.
Heck, even Paradise CA (North of me), which was destroyed by fire entirely and so had many displaced people a year or two after the fire, the city wouldn't approve any area for the siting of trailers to house those who didn't yet have homes.
The primarily motivation for this, uh, bullshit, is home valuation. Home owners, not entirely falsely, believe that a trailer park near them will reduce the value of their homes (so they'll oppose a park even they don't personally think there's anything wrong with them). And there you have it, with home values being a gigantic part of the US economy, they wag the dog of other decisions.
I mean, bless Construction Physics' heart for earnestly trying to find a technical solution to absurd home prices in the US (and some technical solutions are useful) but naturally they have to ignore or gloss over the basic it's all a racket, they want things this way part of current problems.