It's really because we (seattlites) just don't like Californians very much; they are turned on all the time, shifty, and drive super aggressively. Makes sense that he feeling would be mutual (e.g. Too passive, naive, and drive super cautiously). This was a real thing in the 90s at least.
As a born and raised Californian that has visited Seattle via car a few times, I agree completely about our driving habits. There is a reason we drive that way though, it's out of necessity. Our traffic is heavy and drivers are very self-centered so the only way to get anywhere is to be aggressive and take space and position or someone else will.
Personally I preferred the driver's mentality of the northwest and once I had been there a few days I drove much more like them since it was so refreshing to not have to not be in the take and defend mindset. Plus when you want to speed they get out of the way well in advance which is awesome when you're in a hurry.
I've heard many Californian transplants complain about Seattle drivers being so timid, and it really is true we can't drive when it is raining, snowy, or sunny (too much glare).
