Beyond that ESPN already owns Clemson's home conference games for less than they would pay under the SEC pro-rata. They have little incentive to move them to the SEC and pay more for that content.
When you get to the playoff as well (which ESPN owns the rights too) what's more attractive? Clemson as a 12-1 ACC champ or Clemson as an 8-4 SEC at large? Especially when you figure now they're stuck with a 10-3 Pitt as the ACC champ eating up a spot that could've been another SEC or Big Ten team. Clemson & FSU are more valuable properties in the ACC.
One of the things that I think Yormark is betting on, is that football revenue growth stagnates. There are only so many time-slots you can air football games on and there aren't a lot of options to capture more attractive content then the Big Ten or SEC games their partner networks already own. For basketball there are more time slots that can be captured and multiple teams that have brand value still available (i.e. UConn) to create more matchups that can help bring more value to that side of the contract. He's probably correct that it's under-valued, but also faces a need to convince the membership that while football first is correct, the best/easiest place to add value to the next TV contract is probably in basketball.