At one time there were many trains that ran to the Greenwich Yard (South Philly) for the game, including one I took in 1962. But, times changed, and even before Amtrak, it became difficult to justify passenger infrastructure for one use a year. Even the Army Corps of Cadets and the Midshipmen of Navy, who for years took the train to the game, moved to buses. Platforms, catenary, even efficient track connections from the Amtrak NEC to the stadium area are long gone.
As far as I know, the last time a passenger train ran to the Army-Navy game was a special organized by private car owners (led by Philadelphian Bennett Levin) to transport injured patients from Walter Reed National Military Medical Center to the game in 2010. Despite the cooperation by all the affected parties to make it happen, it was a major effort to get the train there, provide a place to unload in what is now a CSX yard and get the injured veterans to the stadium a couple of blocks north.