The 2023 round of major conference realignment was the fastest one because it was the desperate one.
Other recent announcements seemingly came out of the blue, like Texas and Oklahoma to the SEC or especially USC and UCLA to the Big Ten. However there had been talks behind the scenes between the parties for some time before those moves happened. It’s just that folks were largely able to keep their mouths shut publicly until the very end.
The only Pac-12 school ready to bail on the league before this week was Colorado, which is changing leagues for the second time in the last 15 years.