Chicago, and more importantly IL at large, is broken. The state gov is one of the most corrupt in the country. 4 out of the last 6 or 7 governors have went to jail. Dennis Hastert comes out of the IL political machinery. State employees pension funds will likely bankrupt the state as the taxbase shrinks. The job prospects for most engineers are limited. I grew up there and wouldn't move back.
I've only visited Chicago once and really enjoyed it, but I suspect its reputation, whether vaild or not, for crime, cold, and corruption serves as a rate limiter on migration to the city.
Chicago has a nice balance between QoL and CoL; I don't see the huge appeal of moving to the bay when most of it is just overgrown suburb and living costs are out of control
I moved to SF from Chicago and agree that the value for money is nuts there (I loved Chicago), but the extended winter, isolated nature, and the fact that it isn't really destination city for any industry puts pretty hard limits on how much people will pay.
Chicago, as always, begs to differ. But no one notices it, it always flies under the radar which probably contributes to it's success in this regard.