Septa's job is to run without making a loss. Good luck with that.

Subways are insanely expensive, requiring vast public subsidy. Most of the old public transit systems were built by private companies that went bankrupt when the profits didn't match the expectations

Any new subway line is going to be build off the business case that a huge wedge of public money will a financially viable investment due to increased tax revenue from the development it will encourage. I'm sure a Roosevelt Subway would make your life easier, but development is happening anyway, so the money would be better spent elsewhere.

An example of something that *might* make sense is a trolley from Fishtown to the Stadiums. $40bn in new waterfront development, apartments and commerce, all paying taxes to a city that issued the bonds to pay for it