NU has been like this for decades. In the Carr era, I used to frequently update OOC winning percentages for the conference, and only Michigan and NU had better win% in the Big Ten than OOC. For Michigan, that was mostly about big non-con games and, since Carr won the Big Ten 5 times and was almost always in the race, ya know, we were just cool with it. But Northwestern had none of these excuses. Which made it a fascinating outlier.
Wanna know my best guess explanation? Honestly, I think a team like Northwestern doesn't care about ANYTHING in the OOC except experimenting to -- later on -- maximize its odds to be the best it can in the Big Ten. And, if true, that's something that Fitzgerald could have easily learned, for example, from Randy Walker.
The biggest flaw in this guess: That this is an incredible risk to their bowl eligibility; so, why do it? Obviouslt that means it needs to be further developed. But I still speculate that it's partway there.