Lower prices were the result. The real cause is in the story as a throw away - de-regulation.
Regulated airlines couldn’t compete on price, so they competed on service. The last airline to try to compete on service was American “more room throughout coach”. It didn’t work.
All of the legacy US carriers, and most of the non-legacy, either went through bankruptcy or were bought out in the post regulation era.
I don’t know if deregulation itself was a bad idea but the fact that the US Congress kept bailing out failed airlines was. It gave the failed airlines an unfair advantage that made it harder for the “good” airlines to fill planes.