I think many of the things you noted are contributing factors for sure. It is true, however, that the more rural areas are largely more conservative than the more densely populated cities and coastal areas of northern California and I have found that there are a significant number of folks who live those rural areas who don't like seeing cyclists on "their roads."
For example, a couple of years ago was riding a 75 mile route from Foresthill out and back to French Meadows. This is a very remote route with lots of climbing. I would say that I came across less than 10 cars all day. Mosquito Ridge Road is narrow and it has a fantastic 19 mile climb section that is popular with cyclists although I didn't see a single cyclist the day I was riding it.
I was on the final return climb back up to Foresthill when I heard a vehicle chugging loudly behind me so I hugged the edge of the road as best I could. A large, dual-wheeled pickup truck pulling a horse trailer pulled up alongside of me, slowed down and a guy in a cowboy hat screamed at me to "get the f...k off the road."
I hadn't seen a vehicle in a half hour and there was no vehicle coming in the other direction so he could have easily given me space. He didn't because he obviously didn't like cyclists being on the road even though I wasn't impeding his driving in any way at all.
This is not an isolated incident for me in rural areas like that. Don't get me wrong though. I know that the majority of folks in these rural areas are not like that guy. It's just that I've had many, many more encounters like that in rural areas like that than I've ever had in more densely populated areas around Winters, Napa, Sonoma and the coast etc.
I met a cyclist on the American River Bike Trail one day who was from Plymouth and we got to chatting a bit. I told how I really enjoyed riding up in that area. His reply to me was, "I don't ride there anymore. The rednecks don't like cyclists. They'll get you killed."
On a side note, two months ago I hit some uneven pavement on a high speed, downhill, curve and my front tire pinch flatted which is essentially a sudden blowout of the tube inside the tire casing. Well, I went over the bars and hit the pavement hard. I bruised and scraped up just about everything on the left side of my body but the worst was the injury to my rib cage. I'm nearly healed now although my ribs are still not quite right.
I'm getting up there in my years, 75 in a week, and I know the risks of cycling at the level that I choose to participate in it. However, it's a sport that I love passionately. I wish it were less risky but it is what it is and I choose to continue to ride on the roads in the hills as long as I can still do it.