On a number of occasions over the past 10-20 years, commercial flights were initiated into Trenton, NJ, TTN, only about 30 miles northeast of PHL. US had flights to PIT and DCA, Eastwind had a flight to Bedford, MA, just outside Boston, and to BDL, and even UA had a flight to ORD. The airport not only serves Trenton, the capital of NJ, but northeast Phila and all the northeast suburbs, and central NJ, including Princeton, with all of its corporate offices.

It's hard to understand why it didn't work. I flew in there once on US from DCA. It was very convenient.

Also, Wilmington, DE has a decent airport.