I find it hugely frustrating, but it's not that complicated. Ever since prop 13 passed in 1978, homeowners' property tax has been pegged to the purchase price rather than the assessed value, creating a huge disincentive to sell. In a place like LA, most or all of the habitable land has been developed. The lots that are undeveloped (at least those in my neighborhood) are sketchy—steep grades and sandy soil, which will eventually crumble either due to a megastorm or earthquake. No one wants to sell to developers, and why would they? They live in nice houses that get more valuable every year, in a nice part of the country with nice weather. Beyond that, they oppose every housing development imaginable, usually by arguing that "luxury condos" are replacing "rare green spaces." (There's a whole "Save Poppy Peak" campaign near me, which is infuriating, because it's a bunch of people with $1.5 million+ houses who don't want apartments to get in the way of their view.)

There are all sorts of obvious political fixes to this (repeal prop 13, end single-family zoning, incentivize building mixed-use, mixed-income residences, whatever), but I can't imagine any passing any time soon. Homeowners have all the power, fight all these changes tooth and nail (often through lawsuits against developers on environmental protection grounds) at the local level.

Californian's have at every chance voted to make themselves landed gentry. That means low property taxes, restrictive zoning, and often just total bans on building. At a hyperlocal scale it makes sense, allowing things to be built can be bad for the homeowner next door, it just leads to the insane home prices we see now.