I think the Sacred Realm was turned into the Dark World after Ganon touched the Triforce in OoT, since his wish was surely to conquer the world the Dark World became his own Hyrule, then, he built an army in the Dark World and used it to conquer Hyrule in OoT. As you know, when Ganon died in ALttP the Dark World was destroyed, since we never see him die before ALttP (according to the most accepted single timeline theory) we can asume that the Sacred Realm remained as the Dark Word from OoT to ALttP.
Now, as davogones says, maybe the Triforce doesn't fulfill the wishes automatically, it just gives the person means to fulfill it. In this case, the Sacred Realm was turned into a paralell version of Hyrule so Ganon could build up power to attack the light world then, as one of the maidens explains Link.
My theory on the subject, percisely.
Now back on the OOT/LTTP split-up debate...