Yeah football drives the bus. But there's additional value that is unaccounted for. BYU's total earnings from ESPN between their independence football contract and WCC deal probably was more.
Additionally, as some of have stated, a BYU contract with ESPN controlled 6-7 home games against maybe 2-3 P5 teams and a handful of G5/FCS squads. A B12 contract controls potentially as many as 9-10 games involving BYU. So that's at least 33% more BYU football content under control.
Also, without any hard data except for leaked numbers from some of BYU's neutral site games, I have come to believe that BYU was pulling in $1-2 million per home game on ESPN. I also wonder if they were incentivized to play more marquis games and got an extra boost depending on which channel they were put on; ABC, ESPN, ESPN2, ESPNU, etc.
So I think the $6 million estimate is a little low. And yes, the $75 million is probably high as well. But also consider that the whole is greater than the sum of the parts. So BYU teamed up with the B12 is exponentially more valuable than BYU alone. And of course as mentioned above, the B12 deal is for all sports not just football.