Conference realignment is all about money, not wins or what's best for the fans. Oklahoma was the big dog in the Big 12 which they might share with Texas, but not in recent years. They could easily go through their Big 12 conference schedule with 1 loss. When you go 11-1 every year and have a high ranking, fans and recruits are excited. In the SEC, I think Oklahoma could start to decline and become a middle of the pack SEC school. Since Oklahoma last won a championship, the SEC (including Texas) have won 12 by 5 schools: Alabama 6, Florida 2, LSU 2, Auburn 1, Texas 1.
Sure, Oklahoma will make more money in the SEC, but will they win more games, be ranked higher, and fans be happier? No.
Here's a crazy stat. In the Big 12, Oklahoma had the 2nd highest home attendance in the conference. In the SEC, Oklahoma would rank 9th below Texas A&M, Alabama, LSU, Texas, Georgia, Tennessee, Auburn, and Florida.