From what I read, there isn't enough extra money from it to have it make sense.
We all know that nothing happens if there isn't money. I am guessing the math nerds at the networks came back and said there isn't enough extra money to make it worthwhile.
Here is something of interest:
Power Five shoulder programming around Notre Dame games will be key to making such a deal happen
www.cbssports.com
The idea here is that the only way ND can get to $75 million would be to have another conference have games before and after. Let's say NBC bids on the B12 and takes one of their best games at noon, then ND at 3:30, then an 8pm best B12 game. NBC might be willing to pony up for that. That helps ND and the B12.