Maybe global warming will make Chicago a prime destination, especially once millions of folks need to relocate.
But in all seriousness, a lot of folks underestimate the idea of perception. Chicago's weak leadership and rampant crime does deter folks outside of the gated communities of downtown and the lake front communities/neighborhoods in which the high cost of living relative to the surroundings requires higher caliber folks. It's why the suburbs see much better growth in Chicagoland.
I doubt the winters are a massive factor, but schools are. At least in the city proper.
The city is still a massive powerhouse and growing, but the true potential is not really there because of other glaring factors. Considering its a bargain version of NYC for what you get urban wise, that not many other cities can hold a candle to. Chicago offers much but the potential could be much grander...
It just needs the right folks in power there to bring it back to sanity and to attract even more business and residents.