A long distance train serves hot meals from a kitchen the size of a hallway, moving at speed, with no delivery until the terminal. The menu reflects every one of those constraints.
The kitchen is small and moving
A dining car kitchen occupies part of one vehicle, typically split across two levels with the cooking below and service above, connected by a lift.
Everything must be secured. Open pots of liquid on a swaying floor are a burn hazard, so equipment favors enclosed cooking over open ranges.
Convection ovens, steam equipment and flat tops dominate because they hold food in place and produce consistent results without constant attention.
Storage is fixed at departure
The car is stocked at the origin terminal for the whole run. There is no mid-route resupply on most services, and no way to correct a shortfall.
That forces conservative ordering of a narrow range of items rather than a broad menu with uncertain uptake on each dish.
Refrigerated space is limited and shared with beverage, so bulky fresh items compete directly with everything else that has to be carried.
Service periods are compressed
Every passenger who wants dinner must be seated within a few hours, and the car holds a small fraction of the train at once.
Reservations exist to turn the room several times without a queue forming through the vestibules, which is a safety problem on a moving train.
A short menu turns tables faster, since ordering, preparation and plating are all quicker when the kitchen is running a handful of items.
Water, waste and power set hard limits
The car carries potable water and holds its wastewater until a servicing point, which caps dishwashing and therefore the amount of crockery in circulation.
Electrical load is drawn from the train's supply and shared with heating, cooling and lighting for the whole consist.
These limits are why food is often finished rather than cooked from raw aboard, with components prepared at a commissary and assembled on board.
What the format means for a traveler
Communal seating is standard, because filling every seat is the only way to serve the whole train in the available periods.
Meal times are announced by the crew rather than chosen, and they shift when the train is running late, since service has to fit around station stops.
Anyone with a specific dietary requirement is better served by arranging it before departure, since the car cannot improvise around stores it did not load.