You're absolutely right! It's discrimination against solo travelers... and I've encountered this many times on Amtrak! Be sure to call customer relations and complain... that you [and others traveling solo] want the same rights and privileges as couples especially when you're paying for sleeping accommodations... with included meals in the dining car!A Further thought on this... I shouldn’t be forbidden to eat in the dining car because I am traveling by myself. It should be first come first serve for private table reservations in the diner.
These types of crazy rules made up by amtrak staff is why I stopped traveling with Amtrak as much even before covid.