I'd wonder how much of this issue is due to all the forest fires that have happened in Northern CA for the past couple years. Could it be some people are living out of their RVs more if they were unable to rebuild their home, or rebuilding is taking a long time, so they end up becoming nomads? Or they are construction workers up there for all the work available.
But yeah same issue here in CO, anywhere within 2 hours of Denver Metro is really hard to get into without a reservation made well in advance. It is what it is... more people, and they're not building more campgrounds.