If I recall correctly, Sankey had reportedly warned the school presidents against having one media partner control all of their rights, but the presidents wanted the flexibility and longer “look ahead” scheduling windows that would have been available in the all Disney deal. I could have that wrong, but it seems like I remember reading that.
It also meant they don’t have to renegotiate with multiple partners if/when expansion happens. The hodgepodge of media rights deals is why the B1G couldn’t pay full shares to Oregon and Washington when they came aboard. They had to renegotiate 3 different contracts individually and at least one (though likely all) of the media partners balked at the pro-rata, so the new teams get a smaller share. The Big 12 ran into the same issue as well. They have a pro-rata agreement for accepting existing Power 5 teams from ESPN, but not Fox, so any new Big 12 teams have to be re-negotiated for Fox.
The SEC can add whoever it wants and ESPN has pay up as part of the contract. It’s a primary factor that will make the SEC more attractive than the Big Ten when the inevitable ACC collapse happens.