One of the major issues is how the big 12 has structured its first and second tier rights. Each school only has one football game and 4-5 basketball games a year to include in a third tier rights package.
We make a lot of money from ESPN/Fox for our TV rights, but with the high payout we were forced to give up almost all of our content. With only ten teams and so few games available as third tier rights, it is almost impossible to envision a big 12 network. The larger conferences are almost forced to create conference networks because if they did not then a lot of their games would not end up on TV at all. 11 out of 12 games for every big 12 team is on network TV, ESPN, ESPN2, FS1, or FS2. Nearly every game is already on a national channel.
All of TCUs conference basketball games (except one) is on one of the ESPN channels. I think the same is true for almost every single Big 12 team. There really is no need for a conference network when all of those games are already being shown nationally on ESPN family of networks. Yes, there is non-conference season, but most schools have monetized those in some way.
Yes, it would be nice to be able to watch volleyball, softball, baseball, etc on a conference network, but that is not worth a lot of money in the long run. MBB, football, and WBB to an extent are the sports the networks are willing to pay for. The conference networks exist to have a place for remaining football, MBB, and WBB games to be shown on TV. The other sports are just filler content. The big 12 has already sold most of those games in tier 1 and tier 2 rights agreements.