Wasn't there a plan last year to build a stadium in Streeterville or another part of the near-north side?
Chicago is one of the last problem spots for the league, one of the last "why is this team that should obviously be incredibly popular not?" teams along with New England. So many college educated people cycle into Chicago from the surrounding states in their 20s and 30s and become totally enamored with the city (including me next year!), these are prime soccer demo folks. Get even a fraction of the "wtf I love the Cubs now" crowd to start going to games plus add in the ones who are too loyal to Detroit, KC, St. Louis, Cleveland, Cincy, Milwaukee, and Minnesota teams to ever become enraptured with Wrigleyville and you've got a potent mix.