They've been working on the project for two years. Originally, Alexandre Aja was set to direct, but then David Fincher claimed it as his own. And that's when Gaiman and Avary stepped aside. "Once they got David Fincher on, David explained his process consisted of having over ten drafts, done over and over, and Roger and I were sort of asked if we wanted to, if we were interested in doing that. And we definitely weren't."
Fincher is a notoriously demanding director (Robert Downey Jr. once compared working with him to being in a gulag), but no one can question the results. Then again, after spending two years on the script, the prospect of writing ten more drafts can hardly be appealing. If nothing else, Gaiman and Avary's work might stick around -- Gaiman says they left the last draft with Fincher, though he's unsure what will happen to it. "So we'll wait and see what happens. I just hope whatever happens, it's faithful to Black Hole." I think the graphic novel remains in good hands. The tone of the book seems a walk in the park for Fincher. And how far can a story about sexually transmitted mutations stray, really?