Bornakk closes the thread due to caps, but we'll play devil's advocate and try to answer for him: Badges. With Karazhan basically a knockover for even beginner guilds, the only way Blizzard has to control the flow of badges from there is to keep the instance on a timer. The Kara gear might get replaced, but some of the Badge gear has to last for a while, and while Heroics do grant Badges (they're on a timer as well), Kara hands out more of them for free than those old ladies with meat on toothpicks at the grocery store.
Still, in Wrath we're probably looking at an all new Badge system, so you'd think Blizzard might as well open the floodgates at some point. Whether it'll be before or after the next expansion, though, we have no idea.