http://www.freep.com/story/sports/colleg.../30935071/
When the division were being reset after the semi-pompously named Legends & Leaders were to be retired, Sparty requested to be placed in the West division. Apart from the obvious balancing of the divisions competitively, their primary motivation was they wanted to maintain a strong presence in Chicago. Chicago is IMO the white whale of Midwest recruiting for the B1G. It is the most replete with elite recruits in the Midwest outside of the Buckeye State, however unlike Ohio there is no one team that dominates Chicago recruiting year in and year out.
Notre Dame has been the closest to Chicagoland domination going back several decades as they seemed to get the pick of the litter, but times they are achanging. Notre Dame still gets elite recruits but they come from all over the country and are not concentrated in Chicagoland, Ohio, Pennsylvania, and Jersey which provided the bulk of their talent when they were good.
Illinois and Northwestern have played under the shadow of the Midwestern powers and for some reason don't seem to be committed to actually winning football games. Illinois, the state flagship, has no excuse to be as consistently terrible as they have been over the last few decades yet remain in a state of mediicority. They will none the less jump up and bite you every decade or so and Northwestern about the same... but neither have had any lasting recruiting success in their own state which explains a huge part of why they suck for long stretches at a time.
Iowa had some success recruiting Chicagoland when Ferentz was winning but that pipe is drying up because everyone knows the only reason he hasn't been fired is because Iowa doesn't want to buy out his contract.
Enter the gritty coaching staff at Michigan State to fill the void. They have proven themselves as excellent developers of talent by turning overlooked recruits into NFL caliber players. Now they have started to get more and more of the upper level recruits into their program. A big focus of their recruiting efforts have centered on owning Chicago and those efforts are being rewarded. D'Antonio even gave a shout out to Chi-town recruits during the B1G media days. One thing is certain IMO... if Sparty can lock down Chicago, they'll remain a football power.