Planes manage to be economically viable with two pilots because tickets cost on the order of 100 times more than the subway fare and aren't expected to be used

Planes manage to be economically viable with two pilots because tickets cost on the order of 100 times more than the subway fare and aren't expected to be used by ordinary people for daily commutes, and they also travel 30,000 feet in the air so if there's trouble it can be more dangerous and complicated than something that operates on rails on the ground. And even then the need for two pilots is pretty questionable and is primarily sustained for precisely the same questionable reason, i.e. lobbying by pilot unions.