This question was posed to me, and the answer is pretty simple: People in California very often do use their turn signals.
In California, though, the turn signal is a challenge. It has nothing to do with being inconsiderate or laziness. It’s a peacock showing colors, or a baboon showing it’s big colorful butt. It’s an aggressive challenge to the person in the next lane: “go ahead, try to stop me.” The driver in the next lane can either submit to the dominance displayed by the signaling driver, or issue a formal challenge in the form of acceleration.