Having lived in Chicago, I think it's probably because the city government is corrupt, the Cook county government is corrupt, the suburban county governments are corrupt, all their municipalities are corrupt, and the whole region is going bankrupt from it. People look at Detroit, and think Chicago may be next. They don't want to put their eggs in the same basket as a time bomb, or an egg-sucking weasel. The only thing that has saved it so far is that it
is a nice, affordable place to live.
There are billboards on the state border encouraging people to live in Indiana (live in Gary?!) because Indiana isn't going bankrupt.
And it isn't just the obvious form of corruption that everyone can see and hate on, like Blagojevich trying to outright sell a vacant senate seat. It's also the subtle form that pays public employees slightly too much to do not quite enough, and then a pension that gives them even more for doing even less, while their replacement adds even more to the burden. You can't just fire all those people and take away their pensions, because then you can't provide municipal services to your residents, and that is more acutely painful than being slowly bled to death.
Edit:
In slight support of those billboards and some cousin posts, Indianapolis is one of the most affordable cities in the US for buying housing. And the pool for tech talent is largely untapped.
Public transit sucks, though. The city has a huge area and is almost completely flat, so it has taken extreme advantage of its ability to sprawl. Any sudden spike in growth will immediately lead to commuting nightmare traffic, all around the entire city.