Arizona and formerly Stanford (now Cal due to Monty) voted for years to not hold the Tournament, claiming that since everybody plays every conference team twice both home and away that the round robin is more than enough to determine a champion. USC and UCLA joined that cause claiming the same reason. In reality it was mostly due to Lute, Monty, Harrick and later Lavin not wanting an additional two or three games as they were always safely in the Tournament and preferred their teams resting.
However, several years ago Fox Sports came to the Pac-10 and threw a bunch of money at them to get TV rights for a new Tournament to be held only in Staples Center (where FSN could keep costs down due to lack of travel) every year. Once USC/UCLA had assurances that the Tournament would never be held outside of LA they switched their vote and seven years later here we are. Not surprisingly six of the eight Tournaments played in the modern era have featured one of the SoCal schools.