You can read their reasons here:
This is the second year that BLACK GATE has refused a nomination, so one certainly has to admire them for their consistency. And no one can deny that this is a very difficult decision for those, like BLACK GATE, that were put on the ballot by the Rabids without their consent (it is an easy decision for the Rabids themselves and their allies, of course, most of whom are squealing as happily as pigs in shit).
Since I'm on record as urging the "hostages" to stand their ground, I can't applaud this decision. But I will not criticize it either. They had a tough call and they made it, consistent with their own politics and principles.
I will quibble, however, about one of their assertions: that even if BLACK GATE had elected to remain on the ballot, they had no chance of winning. I am not going to go so far as to say they were the favorite... but I think they would have had a shot. All five of this year's nominees were on the Rabid Slate, yes. But two of the five -- BLACK GATE and FILE 770 -- are clearly hostages, slated without their consent. Despite the success of No Award in last year's voting, I think the presence of so many hostages this year changes the equation. My hope is that fewer fans will resort to the Nuclear Option. If so, I think FILE 770 will win here... but BLACK GATE would have given Glyer's zine its strongest competition. Oh, and yes, No Award will be contending too. TANGENT might have a very slim outside chance.
BLACK GATE's withdrawal changes all that, of course. The big question is, what takes its place? Whatever it is, I'd say that it instantly becomes a major contender here, just as THREE BODY PROBLEM became a contender last year after Marko Kloos pulled out of novel. My guess is that the rocket goes to either FILE 770 or the new nominee...
(One also wonders what will take place of the "The Commuter," the Thomas Mays nominee in Short Story. Mays has also withdrawn).
Sixth place has never been so crucial.