Even if "way down" it's still a much bigger audience. That's will the giant audience they already have. The media markets the Big 10 own dwarf everyone else put together. It's not even close.
And a decade from now those same schools will be winning national titles in the Big 10. Because the sharks running the big 10 have outmaneuvered the old boys in the SEC. To help the SEC save face they might absorb the the SEC and disguise it as a merger. Happens all the time in the business world.
Wheels are already in motion You think Texas, Texas A&M, Oklahoma and Missouri have loyalty to the SEC. they'll be the first to go when more money comes their way.