I think a certain critical mass of population was necessary for rail commuter service to exist in the first place. By the end of the war, even Cleveland, New Orleans, and St. Louis only had one train a day (Erie to Youngstown, L&N to Ocean Springs, and MP to Pacific). Of the cities mentioned, only Detroit and Pittsburgh had what could be considered a decent commuter service to lose, and that was predominantly weekday rush hours only. I would say that only Boston, New York, Philadelphia, and Chicago were big enough to rate a 7-day, all-day commuter service constituting a meaningful element of travel within their metropolitan areas.