Wouldn’t it be pretty obvious you never actually boarded your flight to Detroit? They scan your ticket when you board.

Though totally agree you could fly on a different flight under a fake name assuming that the airlines don’t sync up their records with the IDs the TSA scans at the checkpoints.

I suspect there’s other less visible signals that would make this harder. For example your flight under a fake name might be flagged for being an unknown name/person. Also if you’re on the run it’s hard to buy a flight under a fake name anonymously without a paper trail back to yourself.