IIRC, OU’s board had a vote about joining the SEC and they voted no, depending on a few issues. Texas was supposedly entertaining the idea of joining the Big10 if OU left. There were numerous articles about how BYU joining would be the catalyst to get everyone in the Big12 to settle down.
OU and Texas decided not to go the PAC10 that June, but didn’t seriously commit to the Big12 by signing the grant of rights until after TCU and WVU joined.