Given how hot Halo 4 landed, I think 343 just didn't have time. And/also may not consider DLC part of their charter; they make or direct the core game, then seem to farm out other components (such as Forge).
If I'd known 343 were outsourcing the map packs, and to Certain Affinity, I would have not purchased the LE. I ended up giving away the season pass code anyways, but seeing that rocket hog in the Perdition video just made me laugh. That thing ruined Unearthed in Reach, but for some reason CA loves the thing. Though it does kind of fit with Halo 4's BTB theme of random carnage. I've followed the DLC/TU news lightly, and I have to say, I so do not regret getting rid of Halo 4.