Is this a WT sanctioned or approved action?
I think they get carried away since international assemblies are one of the few ocassions they get to express any individuality. You see that with the delegates dressed in supposedly local attire. Some Witnesses use them as an opportunity to express themselves and get carried away.
That's my guess, anyway. I saw pictures from some local kingdom halls where they had literally piled hay on the stage and had the delegates stand for pictures behind it wearing their "local garb."