I think there are a lot of reasons why one area may have more DPC than another. I've heard that here in Colorado we have the most and most of us built up separately from one another, a lot in 2012-2013 without knowing of each other's existence until recently. So I don't think DPC spokepeople or marketing are the reason.
I do think Kaiser etc may be part of it. My aunt is from California and she and everyone she knows have always had Kaiser and she had trouble understanding the need for DPC. Here in Colorado, people generally look down on Kaiser (though I personally go there and have received really excellent care).
I don't think Medical has much to do with it on its own because here in Colorado we have Medicaid expansion too and I still have tons of patients who make too much for Medicaid and too little for "real" insurance. But if there are a large number of people who qualify for Medical and a large number of people who can afford good insurance and not many people in the middle, that could be part of it.
Overhead may be part of it as well. My uncle makes really good money and his neighborhood looks like the poor neighborhoods here. I could afford to buy a house in Colorado only a couple years after my aunt did in California. I mentored a physician who opened in a different part of California and her overhead for the same style of practice as mine is twice mine, which means she has to charge twice a much, which means she has to find patients who can pay twice as much.
I'm curious other people's thoughts. @forestdpc maybe you have some other thoughts?