Why didn't Elgar'nan just...?

...tear open the Fade as soon as he had his new dagger? Was it useless because Ghilan'nain died before they could complete it? Rook was stuck in the Fade prison for weeks and yet Elgar'nan made little progress in his plan to blight the world (he has made SOME since he has the whole mages as blight tentacle batteries thing going on, but I doubt it took weeks to get to that point, and he is miffed about Ghilan'nain's death and yet doesn't release more blight in retaliation? Idk, weird.)

I may have just missed something or misinterpreted his final monologue on the throne though, so if anyone has an explanation I'd be grateful.