O'Hare is a huge pilot domicile for United, American, Eagle, Mesa, Skywest, did I get them all?  It would be interesting to know what the ratio of locals to commuters is for each.
I think many avoid it because when it's bad, it's BAD.  I was never based there, but flew in and out enough to know that there was more times than one that we would be delayed for hours.  Sometimes the ATC flow delays were so long that we'd cancel our flight, skip ORD, and ferry to our overnight city.  I couldn't imagine showing up early for the commute only to see DELAYED or CANCELLED all over the board.  
If you live there, that's another story. The worst case there would be driving into work only to find out your flight is 3 hours delayed because the airplane is stuck in Dayton!
The O'Hare ATC is great, though.  They're some of the best controllers in the world.  They're thrown at the most discombobulated airport layout with arrivals that far exceed gate space.  One little hicup throws the whole thing spiraling- usually it's airplanes around the terminal!!