Also, if you're a fan of the other team you can wear their stuff and not worry about getting grief like you would in Philly and other places.
That's because of the transient nature of the fanbase, which is also part of the problem. I was at Nats @ LAA a couple years ago and a thoughtful Angel fan asked me how DC teams retained fans with so many people from elsewhere moving in. The visiting fan takeover is worst in DC and with the Orioles.
SF fans are more like DC fans in terms of being tolerant of other teams fans, but influenced by the tech industry, there's an expectation of innovation and forward thinking like the Warriors three point strategy, Niners West Coast offense, A's Moneyball, and not being copycats like the Snyderskins were.