In a nutshell, it was highly ubusable in the Doubles, as it had relatively good accuracy for a sleep-inducing move (having the second highest accuracy, second only to Spore) as well as hitting both opponents and having no Pokemon immune to it, unlike Spore with Grass types. The biggest offender of this was Smeargle in VGC- it could utilize Dark Void and the unlimited amount of support moves it had access to to be a major nuisance and was extremely reliable at putting at least one Pokemon at the start of the match to sleep if it as one of the first two Pokemon out. GameFreak probably decided that this was too broken or un-competitive of a move, so they nerfed its accuracy and took it away from Smeargle by only allowing Darkrai to use it. To be honest, I don't know why they had to nerf the accuracy, as taking it away from Smeargle would've been enough to stop it from abusing Dark Void so badly in VGC. Maybe they considered it too broken of a move overall.