They have contracts with CBS, ESPN, and Fox. The latter two are the ones that declined to get into early negotations on renewing the Big12 contracts.
“The general result is that, at this time, with so much uncertainty in the media marketplace as well as the landscape for collegiate athletics,” Schovanec said, “our partners, ESPN and FOX, are not interested in acting preemptively with regard to our contract. They recognize the importance of our partnership, but there’s just too much uncertainty, and they do have four years to go.”
You didn't find that with the SEC and you won't see it when the B1G renews theirs.
ESPN "holding the cards" referred to their partnership/ownership in the SECN and the LHN.