If I'm them, and the deal that includes Oregon and Washington (who have been clear that they're out at the first opportunity) isn't as good as a Big 12 deal would be, I'm looking at options. I definitely wouldn't want to sign a subpar deal that hinges upon programs that don't want to be there.
Signing a weaker deal to provide a stable future is one thing. Signing a weaker deal while retaining an unstable pact is quite another.
Not to mention…<<unequal revenue sharing has entered the chat>>