Is there some reason why they brush passengers aside so insultingly?
Quite often it can be because you just don't know - delays can be very fluid situations, and Murphy's law is quite often in full swing. I've worked flights (in the dim and distant past) where the departure/arrival time of a flight has changed every five minutes for different reasons.
And if the airport doesn't know, it's because the airline (or their agent!) hasn't told them.
re DUS - is it not just changing from a LH to an EWG base, so not much impact?