I'm going to speculate based on living in one of the places that's losing a lot (in very relative terms) of people to Arizona, utah, New Mexico and Idaho, (but conspicuously not to Oregon or Washington,) that this is in large part a generational effect instigated by the way California development has expanded in the past 50 years or so , with entire towns springing up within the space of 5 years around cheap residential RE development tracts.

a lot of these people who are moving originally bought a family home in a new ish (for the time, far-flung) suburb development 25 or 30 years ago for $125-$175k. all the kids have grown up and moved away and they are now selling the grossly inflated slap dash neo-Mediterranean stucco pastiche typical of this area at what they feel is the peak of the market within the curve of their lifetime. Because these giant housing tracts all sold and became occupied more or less simultaneously, everyone who moved in was in similar circumstances and raised families all around the same generational curve. It's no surprise that roughly a generation later we're seeing a surge of out-migration, even without the other factors.

most of these people are going move red states redder and California bluer by this move.