A&M, Arkansas, Colorado, Nebraska, Missouri.
Missouri started flirting heavily with the Big Ten because of "academics"
Colorado lacking revenues much like Maryland which left the ACC-had previously felt more cultural connection to the west and had large alumni base and saw what they thought would be better financial opportunities and stability out west
Several schools including A&M, OU, Texas Tech, Baylor, and Missouri began heavily courting other conferences, making stability at that time very problematic
Colorado moved to the Pac
Nebraska began making overtures to secure their future-the Big Ten listened
The BIG 12 caught wind of Nebraska sniffing around and gave them an ultimatum-jump or sign on--they got the Big Ten to move to add them
Negotiations out west stalled
A&M grew tired of negotiations out west and began talking with the SEC instead seeing that as the best opportunity.
Missouri saw total instability and saw their chances for the Big Ten went away with Nebraska, so began discussions with the SEC which needed a 14th
A&M left
Missouri left
None of that is related to Texas in 2016 working with the conference to move ahead on a BIG 12 network