My hypothesis: it's a direct reaction to so many media and entertainment business being based in California, making it appear from the outside like Californians are especially smug about their state.

From an outsiders perspective, even in HN there have been people saying that if you didn’t like SF then you are just not enough sophisticated nor enough out doors to appreciate it so I can definitely understand where the smugness talk is coming from. But I think it’s a necessary smugness if that makes sense, if you want talent to gather to a specific place you have to be ruthless in marketing for that place, but of course that will create a backlash when people actually visit.

I'd say the entirety of the deep south gets much more hate than California.

because the other states don't suck near as much ass as california