People, especially as they get older, tend to want more space. Being close to nature -- and California, in those rare moments when it isn't on fire, has beautiful nature -- is also a big draw.
The people living in those homes aren't, broadly speaking, lower-class. They live out there precisely because they aren't interested in medium- or high-density housing, for a variety of reasons.
I would say the primary cause is overzealous environmental legislation, brought to you by the same people that have fought tooth-and-nail against nuclear power -- and thus for burning lots of coal -- for the past seventy years.
Clean air is great. I like strong emissions standards on cars and factories. But controlled burns have been absolutely hobbled for years by regulators and environmental groups.
One of my nephews is a firefighter, currently in California. He'll rant your ear off about this.
Light night starts a fire, it burns down a house, who is liable?
Government in the name of fire prevention starts a fire, it gets out of control and burns down a house, who is liable?