On last Coast Starlight trip dinner in diner was not that great. Vegetables seemed like they came out of can food had too much salt meals were too expensive. waiters not very friendly Amtrak offered credit for use on future trips. I don't like policy of having to share table with others. No restaurants do that. Sometimes you meet interesting people but it can still be awkward.
Unfortunately labor costs are very high when you pay crews decent salary for the long hours and time away from home. To maintain old Santa Fe UP and other railroad standards of fresh food cooking meals to order on board decent china and table clothes is also very expensive. snack car microwaved food generally not very good or healthy. Catered airline first class quality meals prepared at central commissaries might actually be cheaper if unions would go along but loss of chefs jobs would make that unlikely.
I'm afraid meals at seat or in room instead of dining car is inevitable