I suspect the real reason why CountryLink are so vague, is to hide any further embarrassment.
Any news about why today's Sydney to Moree explorer is (again) cancelled?
Could be anything - operational reasons is a convenient "catch all" for more specific reasons that Joe Public doesn't understand nor care about. It's not going to un-cancel the train to learn that it was compressor problems, or other maintenance related issues.
I have little doubt that this is a factor too, however my original statement still stands - if you explain a problem in technical terms, you confuse the target audience. Explain it in simple terms, and the target audience is "satisfied" (obviously their train is still cancelled, so they are hardly jumping for joy).
It is not a good look to say that the train is broken down again (and that no spares are available), or that a radio is broken or there is a staffing issue or whatever.... That said, on occasion, they have used the phrase 'mechanical issues' in lieu of 'operational reasons'. Looking forward to hearing what the short-term plans/goals are, once CountryLink are split from RailCorp.
You've just supported my argument - tell the travelling public that the train isn't going to run because the radio doesn't work, and they won't understand why it cannot run. It creates confusion.
Sadly, a lot of problems with these trains are only picked up on train preparation, and this is usually too late to rectify anything but a minor problem - as you state above, the fleet is so stretched that this often means the train is replaced by buses, as there just isn't enough time to rectify the problem.