For one, routing the Cardinal to Boston would require a major schedule adjustment eapecially westbound that would have it serving New York City at an ungoddly hour, and would have it arriving in Chicago much earlier, but not nescessairly at a brutal hour.
One needs to remember the uniqueness of the Cardinal is that it has a very high intermediate turnover rate, with I believe each hosting 3 people on average on the trip IIRC. This means very little true long distance travelers and lower demand for the sleeper.
Another point about the New York routing is that it does carry people from NYP to places in WV and KY, a market that isn't even captured by many airlines.
And, finally, I guarantee you that the general public resists changing trains a lot more than us Railfans do. Every conection is a chance for a missed connection. I remember when the Twilight Shoreliner becane the Federal and only went Boston to Washington, and there was a seperate train that shuttled to Newport News. If 67 was late, Amtrak seldom held the connection, but made those people wait for another train going to Richmond.
As for making the Hoosier a daily train on a different schedule, I could see that being benefical, in the case of an extremdly late westbound Cardinal.