the UCFs, Houstons, Cincinnatis, etc, at their current bottom dollar rates, of course. ESPN presumably values those schools less than BYU, so they would want to pay them the B12 rate even less.

It boils down to this: if there aren't two teams worth more to the networks than BYU, then it makes more sense for them to fork all that new money over to BYU as one of the two new members. If there are two teams worth more than BYU, ESPN isn't "saving" any money on their bottom line by rolling BYU's contract into the B12 contract, because they are enjoying the BYU inventory at a great rate, and paying the higher amount for two teams that will in turn bring in more money for them in the B12.

Like I said, I don't think there are two (available) teams worth more than BYU, so I'm agreeing that it makes the most sense for BYU to be added from their perspective, but rolling the existing BYU deal into the B12 deal is irrelevant.