Because we already got the shock factor in the manga's ending. This movie is merely filling some blanks Kishimoto was too incompetent to address himself.
However something on this scale would shock the ENTIRE fathom, guaranteed.
In the end you could be right, right now it seems like a certainty but as long as there is a smidgen of hope (end pairings for main not being shown in 700) then I'm not going to back down. I know what I'm getting myself into as I've said before, but it's not anything I haven't been through already. I might even already be numb to it.