It became a lot easier to move across the country with the rise of cars and commercial flying, and CA is a really nice place (from a climate and natural beauty perspective, plus the thriving industries). So it may not be the only reason, but I think if prices were equal, many people would choose CA over Indiana for example, if they were looking to move somewhere new.

The relevant metric is did a place become far more desirable to far more people. Which seems obvious when information becomes more and more available, culminating with instant transmission of pictures and videos and forums that create lists of the most scenic or best weather or best beaches, etc.

This is also ignoring sheer population growth, and the unrivaled economic behemoths that have come out of California since the 1950s and produced a ton of wealth for Californians.

Huge population growth without corresponding new home growth.

In the 50’s, the population of the U.S. was under half of what it is now. And lots of professionals (and their high wages) like to live, or must live, in urban areas driving prices up in those same areas.

Supply and demand, combined with “rugged individualism” valued so highly in the states. That individualism is largely what drives NIMBY mentalities.