One aspect of the passenger business that the mainline railroads didn't attempt to recover was that of the corridors, which in the age of autos and airplanes was actually their best chance to revitalize their business. I say this on the basis of my extensive riding of the NEC (especially the PRR part) in the 1960s. Lots of deferred maintenance, old, shabby equipment, unexplained delays, dingy stations. (For example, Baltimore Penn Station didn't have the WW2 blackout paint removed from the skylights until the 1980s.)
Improvements along these lines didn't start until the 1960s and were mostly paid by government funding, and then the railroads in question (PRR, NYC, and Hew Haven) went bankrupt and were essentially nationalized. The current vastly improved service is all a result of this government takeover, and even today there are still problems, like the antiquated overhead catenary on the WAS-NYP NEC. I wonder what the NEC and Empire Service would be like today if those private railroads had spent some serious money on upgrading their infrastructure and service improvements in the 1950s, just like the Federal government did on the Interstate Highway system and the FAA.