They don't want to see.
Gosh. I wish someone would roust all those Reagan voters from their very long naps. Someone needs to tell them that Barbara Boxer and Diane Fienstien are their Senators, and have been for over 15 years. But, you're right. They've those Reagan voters have probably been voting for Feinstein and Boxer because the Republican challengers haven't been "Reagan" enough for their tastes. That makes sense.
Incidentally, while SF may be a small, but densely populated city (the most densely populated in CA), SF's metro area has over 4.2 million, over 10% of the total California population. I wonder how many didn't vote for Obama.