I's a combination of things.
The highway next to the stadium, I-880, is a almost a parking lot at morning and afternoon rush hours. Monday night games start here at 6 PM.- Gridlock. The parking area is a lot less than the Ralph. The BART is right next to the stadium, but only so many people can come on it (the way I go to the Bills games there). The neighborhood near the stadium is BAD, worse than the one that was near the Rockpile. Then Davis is old and senile and meddles in the running of the team. He had Mt. Davis built when he came back and did the PSL fiasco.
The Bills fans are much more rabid than Raiders and 49er fans. I moved here during the Niner's last SB season. I had my windows open to hear the cheering when they won. Not a sound outside. Buffalo streets were a ghost town during SBs and even regular season games. Not so in the Bay Area. The Raiders usually only sell out the Bronco or Chiefs games or Sunday/Monday night games.
The A's get good players and then let them go because of $. But they keep Eric Chavez, who hasn't played a full season in years due to injury. Before they tarped off the top deck for baseball, I used to go to games on Wednesday evenings. A $3 BART ride, $2 tickets in the upper deck and $1 hot dogs. A great time.
See this thread for another reason.