Room service is a delivery business operating inside a building. Everything about how it is organized follows from the fact that the food has to travel before it is eaten.
The trip is the design constraint
Between the pass and the table sits a corridor, a service elevator, another corridor and a door that has to be answered. That is a long time for a hot plate.
Kitchens compensate with covered plates, heated bases and insulated boxes, all of which hold temperature at the cost of holding steam against the food.
Anything crisp suffers most in that environment, which is the mechanical reason fried items travel poorly and braises travel well.
The menu is filtered for durability
In-room menus are usually shorter than the restaurant's and weighted toward dishes that tolerate a delay: soups, pastas, sandwiches, roasted items and cold plates.
Composed dishes with sauces added at the table, and anything depending on a precise temperature at the moment of service, are generally left off.
Items requiring finishing are sometimes sent with components separated, which is why a burger arrives with its garnish beside it rather than assembled.
Order flow is a separate operation
Orders arrive by phone or through an in-room device to an order taker who fires them to the kitchen and schedules the runner.
Quoted delivery times are calculated backward from the trip, so the kitchen is given a target that leaves room for the elevator rather than for the plate.
Late night hours usually shift to a limited menu produced by a skeleton crew, because opening a full kitchen for a handful of orders does not pay.
The tray and the cart are different products
A tray is fast, carried by hand and suited to a single course. A cart is a rolling table with a heated compartment underneath, built for multiple courses.
Carts take more elevator space and have to be retrieved from the corridor afterward, which is a labor cost attached to every one that goes out.
That retrieval is why properties ask guests to call rather than push a cart into the hall, where it blocks a corridor and becomes a hazard.
Why the service is shrinking
Full in-room dining is labor intensive and concentrated in a few hours, which makes it one of the harder food operations in a hotel to staff.
Many properties have replaced it with a limited menu from the lobby restaurant, with pickup lockers, or with arrangements for outside delivery to the desk.
The mechanism is the same either way, and the durability of a dish over a ten-minute journey remains the thing worth thinking about when ordering.