There’s a shortage of pilots that hits regional airlines hard. The large U.S. airlines pay more, and attract pilots out of the regionals. There just aren’t enough pilots to fly regional jets, and American Airlines still has about 100 of those smaller jets parked.
One solution they’ve found to continue serving small airports close to major hubs is bus service. They use Landline buses between Philadelphia and Allentown/Bethlehem, PA (ABE); Atlantic City, NJ (ACY); and Lancaster, PA (LNS).