Why are the Rebbes coming? משהו שמיימי
That seems to be the best that anyone can come up with (see for example למה צריך בכלל את מסע המועצת?) which is pretty sad. The Charedi world in Israel is collapsing under financial strain and this big event is going to cost millions of dollars, wouldn't that money be better used to actually support the poor?
It seems that Satmar will be participating and as I wrote earlier they have some very strict conditions including no speeches in English (except for 1). That won't play very well in NY and the US where except for the Chasidim the rest of the Charedi world doesn't really speak Yiddish any more. What they hope to accomplish is a mystery. This is the reason that R' Shteinman has not really supported this, he understands the situation and doesn't see the justification for the event.