Possibly licensing issues, as Bitt said, however, I could swear they said that the extra money you pay to Xbox to import the RB1 tracks (there was some small nominal fee) was supposed to cover the re-licensing. Plus, if they did re-offer the songs as DLC, they would stand to make *more* licensing money. So that doesn't make a huge amount of sense.

I'm guessing it's more to prevent confusion, to keep people from accidentally buying a song as DLC that they already own on a disc. (That double-jeapordy thing is already a problem with album packs versus single songs anyway.) And also, possibly, to drive up sales of the leftover RB1 discs.

Maybe it's a code compatibility thing: Offering the RB1 songs as DLC might break the RB1 software somehow?