There was an article posted a few years back that tried to determine fan base size for the the FBS schools. I did some manipulation of the numbers in that article and posted it some time ago, but in essence, here's what is shows for fanbase size of each conference.
Big Ten: 18,940,000
SEC: 16,671,000
ACC: 12,579,000
Big 12: 8,354,000
Pac-12: 7,741,000
I believe this shows why a conference network works for the Big Ten and SEC, doesn't work for the Pac-12, likely wouldn't work well for the Big 12, and why it has been a difficult launch for the ACC. If you want a successful network, you need a critical mass of people to watch it, and/or some kind of potential viewer leverage to force it on to the provider's networks. The best TV model for each conference is not necessarily a "one size fits all" deal like a linear network.
Comcast just told the Big Ten that they no longer have the leverage to force it on the entirety of Comcast for the current price. One way or the other, the revenue is going down.