I already cited the numerous tornadoes - then there was the flood a few years back where most of downtown was evacuated.
The tornadoes hit in the suburbs, not closer in near the lake. The 'burbs are not exactly known for areas of looting. And the Chicago flood that was isolated to the Loop and didn't absorb much in police resources. Looting is most likely to occur when the police are distracted, namely with crowd-control or emergency disaster relief.