I'm sorry that happened to you, but the fact is that a majority of people running it these days aren't necessarily doing it because they want to do it. It's an older than dirt instance that is required each week to get one of the current upgrade mats for i120/130 gear. The sooner it's over, the better. So yes, a lot of the time, people are going totally gung ho so they can get back to doing other stuff they'd rather be doing.

If you're in an FC, maybe try putting together a group yourself that'll go at a slower pace or be willing to explain the instance to you. Alternatively, maybe speak up and say that you're new if you choose to just DF it. I've had a lot of instances where you get the "One or more players are new to this instance," but no one speaks up, so the rest of the party assumes people know their role. Lastly, as Wilhem mentioned, try YouTubing a video before entering to get a general feel for the place.

Trying to be helpful, so hopefully some of that was. Good luck!