1.) The Pac 12 is no longer a factor. Its payouts are less than the Big 12, and its network is struggling due to much lower viewership and subscription problems. Even if it pans out, its not going to come near the SEC/B1G networks. Further, the double time zone thing is a killer for Texas teams in the Central Time Zone...they considered overlooking that back in 2011 but along with complications related to the LHN, it was a non-starter.
2.) Nobody is leaving the SEC.
3.) Houston has no chance of getting into the Big 12 because Texas does not want 5 in-state teams. Likewise, teams like Boise State, Colorado State and Air Force have zero chance. Anyone bringing up such suggestions needs their head examined.
4) The ACC makes far less than the Big 12....making its high end teams vulnerable to cherry picking from the SEC/B1G.
5) The B1G/SEC want new states with large populations to expand their TV networks...that is their fiscal model...and that makes ACC states/teams highly desirable.
6) KU/OU/UT...and maybe WVU...make more money than ANY team in the SEC or the B1G. That will not change until well into the 2020's, at which time new contract negotiations will start for the Big 12 and new expansion candidates will have likely come available. THAT is why the league is stable.
These are the basic facts, so arguments that do not accept these assumptions are specious.