I can’t speak to the specifics of that date (IU game), but because of the late addition of Washington and Oregon, the 2024 schedule had to be redone last fall and some dates at the old soccer stadium were not available. As temporary client, the venues were not interested in burning ongoing relationships to cater to Northwestern.
Also, once the commitment was made to doing this, a higher priority was given to playing as many games there as feasible, especially to accommodate the student body, but let’s face reality, there are 5-6 schools that drive revenue for Northwestern home games and Indiana just isn’t one of them.
You are also going to have to tell some season ticket holders they may need to sacrifice not going to a game or two. You can make that case if the opponent is Eastern Illinois or Duke but you can’t do that with Ohio State or Illinois.