The Green Head Of Greed.

The world engine can't be controlled so more power is being provided by it to the law matrix, and the law matrix wants to expand thanks to it. If they allow it to expand however it wants, it will destroy Legion-1's inner world, and they might never be able to take control of it.

What they are trying to do by limiting it is to buy time for them to gain control of it and apply the pressure required to keep it within proper parameters. Legion-7 has joined the law matrix as the controller. It is his presence that is doing the bulk of keeping the law matrix still, so the seven of them are not instantly overwhelmed. The death of Soverick is to provide the power outlet. 

Soverick died, but not really. It was the version formed by the tentacle of Legion-7 that died. The destruction of that body meant that he had returned to Legion-7. Since Legion-7 is currently in the law matrix of the incomplete world fragment, Soverick also returned to the law matrix.