Its simple, if the Big 12 expands, it means the war is over and we have lost. Expanding the conference with the like of Cincinnati, Rice, SMU, Houston and the rest of the AAC does nothing with the networks along TV money lines. It just doesn't, The remaining Big 12 school would have now joined these other schools that become the walking died. Go look at the USA Today financial athletic breakdown of the schools that you are talking about, they are all being kept afloat by their university pumping in 10's of millions of dollars a year to keep their athletic departments up and running. No way the State of Iowa BOR is going to allow ISU to do that year after year. I am sure, most of the other remaining Big 12 members are in the same boat.
The remaining 8 schools either get picked up into an existing P5 conference, or they die as a program, financially. Big 12 goes from paying out $40 million per school to $20 to $25 million per year. ISU could not handle that big of a yearly drop and stay competitive like we are now.