Philadelphia is the largest city in the Commonwealth of Pennsylvania and the sixth-largest city in the US, spanning 142.70 square miles. It is the second-most populated city on the East Coast, second only to New York City, which boasts a population of over 1.6 million people. However, a city this size still proved to be too small for Marvel's most violent vigilante in the story "Six Hours to Kill" that appeared in 2009's Punisher: Frank Castle Max #66-71(by Duance Swierczynski and Michael Lacombe). This story brought Castle out of his usual base of operations in New York City and into Philadelphia for one terrifying night while simultaneously explaining why Frank chooses to work primarily out of New York.
A lead on a child trafficking ring brings the Punisher to Philadelphia. At 10:05 PM Castle arrives at the building used as a front for the operation and guns down the men running it. His work done, Frank returns to his van only to be gassed and rendered unconscious by a mysterious figure in a trench coat and gas mask.
The Punisher awakens in a lab, restrained to an operating bed where he is injected with an unidentified poison that will kill him in six hours. If Frank wants the antidote, he must kill one specific man before time runs out. Castle agrees and is released, just to snap the neck of his captor. At peace with his pending death, the Punisher then elects to spend his final hours killing as many criminals as possible.
The following six hours are filled with blood, bullets, and corruption, all spiraling down to a single firefight. As the Punisher crosses names off of his list of local criminals he becomes the target of local mobsters, street gangs, crooked cops, and even federal agents. Throughout it all, Castle manages to cure himself and bring the men responsible for poisoning him to justice.
Throughout the story, the Punisher makes frequent remarks about how small Philadelphia appears. The fallout from one night’s worth of work is testament to his opinions on the city and how impossible it is for him to operate effectively in such a confined area. Philadelphia is a large city, but it is dwarfed by New York.
After eliminated a single building of criminals, Frank is made a target of nearly every criminal in the city. He expresses his frustration with the situation, lamenting that there just aren’t enough high value targets for him in Philadelphia. In his opinion, Castle clearly felt that operating in a city like Philadelphia was simply a waste of this time and talents.
"Six Hours To Kill" answers the question as to why the Punisher primarily chooses to operate in New York City; the surrounding cities are simply too small for his tastes. New York City is massive enough that a single night of waging war on criminals grants Castle the room he needs to slip away into the shadows. Philadelphia might be a nice place for him to visit from time to time but, as Frank states at the end of story, one night in the City of Brotherly Love is enough for him.