That's poor inferential logic on your part. For once, this is San Francisco and people are a lot more metropolitan, liberal and culturally accepting than let's say a school in Mississipi. Secondly, when you interview you don't really know whether you will be interviewed by a 30 year old faculty member with more liberal views or by a 65 year old conservative dean for example. Why take a gamble ? For what ?
People from MS are nice people. Well, at least the ones I met were really nice.
But yeah, I've heard that CA people tend to be a bit more liberal.