I was thinking through which trains were still running with Heritage dining cars. Let me know if I missed any...
Crescent, Silver Star, Silver Meteor.
So, why is it the dining car was taken from the LSL and not another train?
To be fair, the same question could have been posited should the dining car have been removed from one of the other trains.
In any case, if I recall correctly, the decision was down to either the Crescent or the LSL. While it was never made clear to me, I believe they opted for the LSL because they felt the schedule for that train was better for a temporary downgrade in service (not to start that debate up), and because there would be an easier method for dealing with bad ordered cars and needed parts in Chicago (remember the Cardinal also runs out of CHI with Diner-Lounges).
There may have been other reasons, but that's what I recall off the top of my head.
Rafi