Biographical: Jarom gives us little personal information, but he does indicate that he has prophecies and revelations, but declines to write them. We can therefore reasonably assume that Jarom is a righteous man attempting to follow the way of the Lord.
Textual: Jarom's reason for his little writing is not that he does not have revelations, but rather that "these plates are small," and that his prophecies confirm those already written. Certainly many prophets have spoken and written on the same themes as other prophets, and their words are all valuable. We must look first to his assertion that "these plates are small" as the reason for his compact statements. When combined with Amaleki's final statement that the "plates are full" (Omni 1:30), we may freely assume that both Jarom and Amaleki are discussing physical limitations of the plates.
The best hypothesis for these statements is that Nephi made the plates, and when he made them, made many more leaves than he used. All other writers on those plates wrote on the physical plates that Nephi had created, and they did not create any new plates. Indeed, with the increasing marginalization of Jacob's lineage from the rulers of Nephi, and Jacob's polemics against the rich, we may suggest that Jacob's lineage did not have access to the resources to create new plates to add to the set upon which they were writing. By the time of Jarom there are few sheets left, and Amaleki fills them up.