Earlier quoted context omitted.
Like many other problems in California, this one can be largely traced back to a single source: Proposition 13
Which was created to combat the problem of grandma kicked out of her house because she can't afford her property taxes. How do you get around that?
If the law allows it and the regulatory compliance costs are low enough, maybe grandma can take out a home equity loan and turn her 1-story ranch into a 3-story apartment and take advantage of the cash flow. If she needs a little more, and her neighbors are also having trouble paying their property taxes, they can pool their resources together and build an even larger apartment block to replace their old houses. Win-win for everyone, except for busybody NIMBYs who care about "neighborhood character" to the exclusion of everything else.