Nephi's apocalyptic vision is sufficiently comprehensive as to show a vision of John the beloved, and to indicate that part of John's mission would be to write concerning the events of the end of the world. Nephi's vision of the end emphasizes the particular perspective of his lineage, but it is not limited to his descendants, nor to the New World exclusively. In order to understand himself and his progeny in the proper context, Nephi is shown the events of the end which include the Old World.
The apocalyptic writings of John demonstrate no such global awareness. Where Nephi specifically sees the future history of two hemispheres, John's vision is global without distinction. Why might there be such a division? Why would Nephi's vision be more explicit than that which John recorded?
The answer is necessarily speculative, but John was a child of the Old World only, and his apocalyptic vision provided the essential information on the future history of the whole world without reference to another hemisphere (which he may or may not have seen in vision - remembering that the Lord intended to keep the New World from the knowledge of the Old for a time). The difference with Nephi was that he was child of both worlds, with concerns for the future of both. Thus it was relevant for Nephi to comprehend the interaction of the hemispheres, but not so for John.