Even without being able to vote, the Dark One has been in a fairly strong position throughout the voting process.

1. There was/is a 50/50 shot of the world ending and, by extension, him having a chance of making goblin lives meaningful.

2. His high priest is off working on the plan that no only caused this vote to occur, but has a better than 50% chance of guaranteeing that the next world will be more favorable towards goblins and even a stronger position among all other deities/pantheons (by his way of thinking, either he gets the ultimate bargaining chip or the world starts over).

Ultimately, it seems he'd rather rework the world as is, and not condemn the lives of the goblinoids for a power gain if it can be avoided. However, he's also willing to play hardball, and if sacrificing the goblins in this world will make goblin life better for all time in any potential future worlds...