I can’t imagine dorms, dining halls, or campus in general are much (if at all) worse than at other schools, and as we have seen other Chicagoland schools have higher scores so weather doesn’t seem to be the factor either. Getting the Lake Effect - colder weather and more snow in the winter - might have some small effect though. I would next have thought that the quarter system would be responsible, but DePaul and UChicago are on the quarter system as well.
Maybe Northwestern is just really stressful compared to other schools, or people don’t like the social situation, or the survey collecting the information might be flawed (wording for instance).
This is a very interesting phenomenon and I do wonder what caused/causes it.