Fox owns 51% of the BTN. The Big 10 owns 49%.
The SEC does not own any of the SEC Network. ESPN pays the SEC a fixed amount.
The PAC 12 owns 100% of its network.

The ACC and Big 12 don't have networks.

The Big 10 is making tons of money with its network. The SEC gets a nice paycheck every year for its. The PAC network is struggling but long term prospects look decent.

I think the ACC would have moved forward with something similar to the SEC if ESPN were a willing partner. ESPN's budget cuts may be holding that up. I doubt the ACC wants to go it alone like the PAC.

For the Big 12, the window for forming its own network may be closed unless they can convince Texas to transform the LHN to a Big 12 Network. I guessing ESPN will push for that.