You had NU, UChicago, and Notre Dame in the larger Chicago area. 1 made little commitment. 1 went all the way to D3. 1 focused on it. Lots of non-alumni view it as their team.
Plus to many people in Chicago who never went to college or went to a college without major football they latched on to Notre Dame as their college football team. Northwestern really could of been Chicago's team for all of those people but losing for years does nothing for that. I had many friends back in the day from my neighborhood who went to DePaul, Loyola, U of Chicago, Lewis University, North Central, etc. and we would make a yearly trip to an ND game during college since they were all fans. It was about 7 to 10 of us who did this for about 8 years running during and after college..we even made a trip to the big House, Spartan Stadium and Purdue to see their beloved Irish....I begged them to come to NU once while in school and they did and we got pasted by Sparty 76-14...tailgate was fun so was the throwing of marshmallows but .no one would come to a game again with me until the '95 Penn State game