As recorded in Jn 21:21-23 and DC 7, John the Beloved was translated just like the three Nephites. Like John, the reason that their desires were granted was because they had great faith, And it was by faith that the three disciples obtained a promise that they should not taste of death; and they obtained not the promise until after their faith. (Ether 12:17)
Wilford Woodruff
"To these three Jesus gave a promise similar to that which he gave to John the Revelator--namely, that they should tarry in the flesh until he came. History informs us that the wicked tried to kill John in various ways, placing him, on one occasion, in a cauldron of boiling oil, but his life was preserved; and that finally, in the reign of Domitian Caesar, he was banished to the Isle of Patmos to work in the lead mines. While there he was blessed with visions, revelations, knowledge, light and truth, a portion of which we have recorded in what are called the Revelations of St. John. In the reign of Nerva John was recalled, and afterwards wrote his epistles. The first quorum of Apostles were all put to death, except John, and we are informed that he still remains on the earth, though his body has doubtless undergone some change. Three of the Nephites, chosen here by the Lord Jesus as his Apostles, had the same promise--that they should not taste death until Christ came, and they still remain on the earth in the flesh." (Journal of Discourses, 13:320)