Giants had the right to San Jose and kept them out of there, so there's some historic bad blood.
I live in Santa Clara County, used to live in Fairfax County, and this area is nothing like DC-Baltimore. The Giants own the fanbase here, far more than the O's did DC/NoVA pre-Nats. Sports bars throughout San Jose/Santa Clara/Mountain View are all in on the Giants, very little A's support. CalTrain, which is commuter rail and runs frequently, ends across the street from Oracle Park, with stops throughout Silicon Valley, tons of people around San Jose take it to Giants games. MARC in DC/Baltimore is nothing like that. And fans in the East Bay just past Oakland in Orinda, Walnut Creek, etc are also all in on the Giants, even though they're closer to Oakland. Walnut Creek has a Giants store and is mostly SF fans. The A's would have had an uphill battle winning over fans in San Jose even with a move.
While it's much closer to SF than Baltimore is to DC, Oakland has a Baltimore problem in that the corporate market in SF and Silicon Valley is much, much larger. One reason the Niners moved to Santa Clara was the presence of all the tech companies that pay top dollar for suites and boxes. The A's, like the Raiders, are a working man's team, their core fan base would have screamed if they had to pay higher prices due to tech companies pushing up prices. Much like Baltimore, Oakland is not really a Major League city, and the move out of the region makes sense, especially when so many East Bay fans are hard core Giants supporters.
