In the real world, nothing has one simple cause or one "only" solution. The housing problem in California, and elsewhere is complex. This is akin to people who say, "The problem with homelessness there has one simple cause..." and then insert their favorite boogeyman.
There are many factors involved, other than NIMBYs, and BANANAs (Build Absolutely Nothing Anywhere Near Anything). There is corporate greed, geographic restrictions, land use issues, transportation issues, tax issues, and the list goes on and on...
The loudest among those on HN seem to be BEASTs (Build Everything to Achieve Skyscraper Town). That's not healthy, either.
† Amusing field guide to various types of NIMBYs: https://www.chicagoarchitecture.org/2015/08/19/a-field-guide...