Most people in JP server join a DF expecting to get a kill.
This is basically it. It largely has to do with cultural differences. In the west typically everyone has an "I'm here for me" attitude, which means that when you mix a random group of people together, some are going to be there intending to clear right away and get done - and others are going to be ready to wipe for an hour to learn the fight blind. A different attitude towards community in Japan however generally leads to people sharing an understanding that they're all there to get it done and cleared; while help will be offered, it's expected and understood that you're ready for what you're getting into. If it's not meshing, it will end quickly and move on.