"cynic mode on" Perhaps they dont want to sell many or any of the perishables at full price, so as to have more left to sell at half price to friends or off duty staff.
It would not be well to state that none are left, since that would be a blatent lie, and clearly untrue when the items are then offered cheaply later.
Not placing the items on display would however discourage sales without telling any lies.
If challenged by management about the lack of goods on display, it would be a simple matter to make up some excuse such as "forgot" "no time" or "fridge not cold enough"
There are issues with the electrical circuits on some catering cars and fridge modules are notoriously unreliable. As perishable foods have to be stored within a strictly temperature controlled environment, (monitored and recorded by the Train Manager), such goods have to be stowed out of sight in working chill cabinets when display cases malfunction. The above insinuation that this is a deliberate ploy is arrant and offensive nonsense.
Operational staff tend to take meals with them to work. There are microwave facilities in nearly all mess rooms and often a full kitchen facility as well. For the less provident, or "friends and off duty staff, "late opening convenience stores mean that food is available more cheaply and with with more variety than even reduced price railway goodies.
Believe it or not, an overwhelming majority of customer hosts deplore waste and will do everything within their power to avoid destroying perfectly good food. (This is done under controlled conditions at terminating stations). Price reductions do little for the budget, but do ensure that waste is to an extent, minimised.