@Londonee, McGrath, et al.
I don't think we should underestimate daily usage of Megabus and Bolt Bus to DC/NYC from Philly.
The advantage of the buses of course are costs. Amtrak is pricey and geared towards more business travelers. I think each transit serves somewhat of a different market based on price points. And, a lot of working class folks (making min. wages or a little better) come down from NYC to work in Philly using these buses on a daily basis.
Found this interesting read. I quickly skimmed it. But maybe Londonee, mcgrath, and others who are debating it should take a closer look. There might be nuggets of info in there to substantiate each's claim.
The Size, Scope and Competitive Statusof Express Coach Carriers in the United States
https://editorialexpress.com/cgi-bin/conference/download.cgi?db_name=TRF18&paper_id=19