Here's my take...
Their biggest issue is that the SEC and BIG10 both have schools that nobody cares to watch outside of the radius of that school. Missouri, Vandy, Miss St, USCe, Kentucky, Purdue, Maryland, Rutgers, Northwestern, Minnesota, Illinois, these are all teams that bring nothing to the table. It's a flawed model from the start. If you want to break away and reform college football you don't bring Rutgers with you.
I personally think the entities that have the real exposure are the SEC and BIG10 themselves. What is stopping a group of 40-ish teams from all agreeing to leave their current conferences and start their own league, leaving behind any dead weight that the conferences won't be able to jettison? If you did it this way, a group of early movers that are the top teams in college football could go find the other 30-40 most valuable teams that would maximize the TV contracts. There is a combination of teams out there right now that would earn the most eye balls if they formed their own league, and it's not a merger of the BIG10/SEC.