I've been following the A's stadium situation for years, mainly just because it's been such a trainwreck of sorts. I've gotten the impression that given the opportunity, either team would have jumped ship at the slightest opportunity, leaving the other team in the Coliseum all by themselves. In the end however, they're both gone.
Earlier in the 2000s, there was a plan to move the A's to a new ballpark in San Jose, sponsored by (and named after) Cisco Systems. Ultimately, it was the S.F. Giants that sabotaged the move, citing an obscure agreement (probably dating back to the 1960s) that mapped out all of the Bay Area as either "Giants Territory" or "A's Territory", I assume based on broadcast TV coverage areas at the time. As it turns out, San Jose is in Giants Territory, so they they were able to block the move. I think the Giants just preferred the A's to stay where they wanted them, in the crumbling Coliseum.