Ah that makes sense then.It's not free. It's paid DLC. It's only free if you got the limited edition disc that comes with both.
For Europe and Australia they also released a unlimted version featuring both games on one disc. It's part of Nintendo Selects. Idk why they skipped the NA region for such an important release, but Australia for some reason also didn't got the Selects version of 3D World...