Ever since the announcement they were doling out on disc-content, I hypothesized they were doing so, in addition to the map and mode rotation, in order better control and research content. By control I really mean control of situational issues regarding the game rather than play parent. A lot of the time you see content released you also see small patches here and there. All the refinements would probably head toward a sequel as well as stronger understanding of the online community and online in general.
They could very well easily unlock it, but they still want to dole out more stuff and refine it, or they may be waiting for the sequel to do it. Obviously this is seems silly, liking into Nintendo's overall online growth, it apparent they still need improvement. Additionally, due to Nintendo's... precision in hiring employees and the growing development of games and platforms, this might be their way of better addressing this issue.
Obviously not the best tactic but its better than doing anything. Also I have a inkling that there's no way this rotation issue hasn't been brought up to near-death.
