I would say "all of the above" as well as politics and cheaper taxes from everything that's been mentioned. The influx of Californians and others into Idaho is a source of great ire here in Idaho since it made housing prices skyrocket and practically stopped renters from ever being able to become home owners. The topic is on the news even more than the missing children here, specifically because it's such a high emotions piece and gets people arguing. Car stickers with "Go back - We are full" are not an unusual sight.
The reality is that the entire mountain west along with Washington and Oregon have been complaining about Californians invading and having what they perceive as negative impacts on their state, causing real estate prices to go up, etc. since at least the 70s.