The parts of California which don’t have a housing problem are, broadly speaking, the parts of California which aren’t attractive to a ton of people as places to live.
The root cause is prop 13 disincentivizes moving around keeping the supply illiquid, and encourages ninbyism preventing new construction, as you’re basically locked in whenever you currently live.
Not just prop 13, but the capital gains part of the tax code.
Used to be you could sell your house for more than you paid and have 2 years to roll it into buying a new house for the same or more money. Now the difference is taxable capital gains regardless of what your new living situation becomes.
