I presume they are referring to the airline deregulation act of 1978. There used to be dozens of regional airlines whereas now we notably have 3-4 giant corporations after decades of aggressive mergers and acquisitions.
You’d be surprised but there are still regional airlines. This is because a company like delta franchises some routes basically. You might go on a delta flight and ride on a delta plane, but the operating company is some almost unheard of regional one.
I’d guess also you wouldn't have to handle the maintenance end of these smaller planes eg. your bombardiers and what have you if you’ve spun off all those flights