There are a number of reasons drivers flee after an accident in the Chicago area:
Some drivers may be under the influence of alcohol or drugs, and they fear a DUI charge.
They may also fear being charged with other vehicle crimes associated with causing injury or death while under the influence of drugs or alcohol.
Some drivers may be so intoxicated that they do not even realize that they have caused an accident, and drive away oblivious of the havoc or devastation they are causing.
Other drivers may flee because they are driving without a license, driving without registration, or driving without insurance.
Some may be driving a stolen vehicle, or they may be wanted by the law for some other offense, like an outstanding warrant.
Others are simply fearful about what they have done, and are afraid to face the consequences.