They haven't recruited Illinois (more specifically, Chicago suburbs) well enough. Considering the hockey growth (in terms of minor hockey participation and NCAA player production) in Chicago Metro since the Blackhawks 3 Cups, Berry never went after those kids hard enough. Problem is that with many of them growing up in wealthy Suburbanville USA, they're not as likely to covet North Dakota because Grand Forks is small town, Upper Midwest, much more rural, relatively speaking.
The Chicago suburbs kids like Wisconsin, Notre Dame, Michigan, Michigan State, Denver, Boston University far more because those schools are either regular Midwestern university towns and/or are in bigger cities. I think Berry once touched on the fact that North Dakota has had problems recruiting big metro, non Upper Midwest/Western Canada kids, which would be places like Boston, Chicago, New York, Toronto, Los Angeles, and to some extent, some Vancouver because Grand Forks is so so different culturally from those metros.