On a crowded train, what good does it do to know whether someone who is standing in front of the door is getting off or not?

That does not excuse the rude response from the CO employee. However, my experience is that you're wasting your time asking.

Just wait for the doors to open, and then if the person doesn't move, say "excuse me". The person will briefly step out of the train or move back so you can get by.

One time on the NYC subway I was standing between the door and a vertical pole. It was crowded but not packed; another passenger next to me had a bicycle with her. Her bicycle was wedged between the pole and the end of the car.

As we were approaching a station, she asked me if I was getting off at the next stop. I replied "no" and continued to stand there. After a few seconds, she started to get irritated with me and said "Could you move? I'm getting off at the next stop." I said (nicely), yes, I will move as soon as the train comes to a stop. Stepping around a bicycle on a slowing train is an invitation to trip and fall.

Whatever the situation, after the train stops, it takes only about one second to move, and it takes about a second anyway for the doors to open after the train stops.

Naturally, airport trains tend to have much more luggage per person than a city subway, but I believe the same thing applies. Actually, if you don't have luggage yourself, you can try stepping over someone else's luggage (or jumping if you're short ). I've done that myself a couple of times.