Someone on YouTube explained it well:
"it seems here [in CA] we are a group of fish trying to get to a spot together quickly and efficiently. In Utah it's all people for themselves and then you end up on traffic jams because of one dick weed that wants to prove a point. Pay attention, they are fast paced, but they drive like your a team. not a one man marathon"
I'm not sure if CA is unique in this or not; it's the only place I've driven where I've experienced that teamwork feeling while driving. Colorado was close, in that they didn't view other drivers as enemies, but they didn't particularly function as a team either. My experience was that in CA, people will be looking a quarter mile ahead, they'll anticipate someone else's lane change 10 seconds before they put their blinker on to change lanes, they let them in, when they change lanes they accelerate so the person they pulled in front of doesn't have to brake, they don't tailgate because they realize it is unsafe, harder to read other drivers, and adds to traffic. It feels like everyone on the road is playing on your commuting team (not against you). If you're a less attentive, less aware driver in California, you're going to get honked at. It's their way of saying "hey, we've got a good thing going with this team, you're not paying attention, and your bad driving is screwing it up for everyone." It's not a hateful honk of the horn, rather a quick correction. At least that's how I saw it when I lived there.
I think Californians get frustrated when they go to other states because they expect other drivers to have an equal level of situational awareness. There's simply a different culture, and when those cultures clash, everyone thinks their culture is right and the other is wrong. Maybe it's because I grew up with the California driving culture, but it sure felt good to be back there where people drive like I do. I remember taking a week long road trip to northern ca with LOTS of driving. At the end of the week, my wife and I reflected on how I didn't get frustrated even once with another driver on that entire trip. It must be because I was back in the driving culture I grew up in. I wish I could go a week... or even a day in Utah without getting frustrated by other drivers on the road. I realize that says more about me than the other drivers, but it's been an interesting observation as I travel to different states.
Now... when you add snow and winter driving to the list of skills, CA drivers fall miserably short (which makes sense since they've never experienced true winter driving before).