Sadly the scenario described is what happens on many services.
St Pancras - Sheffield on East Midlands can be excellent but has all the problems of covering trolley, first class service and any buffet.
XC Newcastle - Sheffield, trolley may not come round until after Doncaster - might as well wait to get home. 1st class may fare slightly better.
XC Sheffield - Newcastle, trolley comes as soon as I sit down on the train after breakfast. Doesn't call again until 2 hours later crossing the Tyne.
East Midlands Sheffield - Norwich trolley leaves at Peterborough just when ready for a drink on a long journey. Was good on Sheffield - Manchester leg last time I used that service having been unable to get aboard the preceding TPE - the trolley was struggling to get on.
TPE Sheffield-Manchester either direction, trolley usually seems to be marooned in 1st class unable to move even in there (assuming there was one) and leaves/joins at Doncaster.
My best memory of train catering was from Fort William having a 3 course meal across Rannoch Moor in 1958, my father and I possibly the only diners that day. I had sole as my main course.
If the train is quiet trolley or buffet sells little. If the train is rammed it's likely to be a similar economic result. It's only when the train is always modestly loaded for the greater part of the journey, and catering is guaranteed to be there, will passengers rely on it and consistently buy.
That said catering staff vary in their approaches. On my most recent encounter the operator sauntered down the train looking totally bored and flatly reciting a list of things he had without looking at anyone or slowing his sedate progress at any point. Didn't expect to sell anything, and didn't.
My first HST experience was about 1976/7 from Paddington. The young lady there was brilliant. Smiling all the way, stopped at every seat, eye contact, "would you prefer tea or coffee sir?" Train 75% full, everyone bought. Expected to sell, and did.
Very difficult to manage staff in such variable conditions and losses almost inevitable on most trains.
