California has an overwhelming left-leaning majority that probably loves the idea of universal healthcare. But even if you don't want to take the whole of California (which still has a large conservative presence in its rural areas), you could focus on select counties or cities like SF, which are undeniably overwhelmingly progressive.

Why don't they implement Universal Healthcare on their own (since getting the entire nation to go with it seems impossible). They have a progressive supermajority that I'd imagine wants it, as well as an absurdly high GDP to support it. So what's stopping them from doing it? And conversely, it seems to me that if even California won't go for it, then the mere hope that the entire nation would go for it seems absurd.

The only explanations I can think of is that I incorrectly assumed liberal Californians overwhelmingly want Universal Healthcare, or that those running California are in the pocket of insurance companies and special interests (and so refuse to make it happen). Or maybe I'm just underestimating the practicality of a single state/district having Universal Healthcare on its own?