They probably have to act all together to unmake the world without the Snarl escaping. And they have to follow the rules, and they are split nearly 50/50 on the issue. And the Gates may be a new thing.
Some of the graves appear bigger than graves "in front" of them. Assuming this is not an error I ownder why a world would get a bigger graves than another? More people on it? Its souls were nommed by the Snarl rather than killed by the Gods?