Because Fox (11CT), CBS (2:30) and NBC (7:00) are paying top dollar at those time slots- they rotate who picks 1,2,3 each week. Each of the networks is going to want the premier matchup at their time slot.Good point, might be part of the reason rumors are that many B1G ADs/presidents are in no rush to add more schools.
So it seems to me if ORWA are added to Big10, an existing or new media partner may need to be creative to add a 4th exclusive, high viewership window.
It might be easier for Big10 to get Amazon or Apple to pay $75-100M annually to stream 13-15 games. But NBC, CBS and FOX might also be willing to add some more $ to their existing deals because adding the ORWA brands creates more great matchups for them to choose at their 3 spots.