This is the perspective of someone who doesn't understand how most people in the US live. Air travel is not affordable for many people.
To travel from NYC to Chicago on Aug. 21st:
Flight: $124 nonstop (2hr 40 min) or $85 with layover (7 hours)
Greyhound (bus): $170 (23.5 hours)
Amtrak: $144 (19.5 hours)
If you value your time and/or your money the flights usually win