The small plates of Nephi were fashioned by Nephi thirty to forty years after he left Jerusalem (2 Nephi 5:28-34). They were fixed in size and number. They were passed down originally to “write the things of my soul” (2 Nephi 4:15), then to write “a few of the things which I considered to be most precious” (Jacob 1:2), and then “that our genealogy may be kept” (Jarom 1:1), or “to preserve our genealogy” (Omni 1:1).
As a physical artifact, the plates play a role in their writing. When Amaleki ends the record, the plates were full (Omni 1:30). In the English text the record just exceeds 142 pages. Although we do not know the original language of the plates or their original extent, the English will be roughly proportional. Nephi takes 116 ½ pages of the record, amounting to 82% of the record leaving 25 ½ pages. Jacob takes another 18 ½ pages, or 73% of the remainder leaving 7 pages. Enos takes another 3 pages or 43% of the remainder, leaving four pages. Jarom takes about 2 pages, about half of what is left. Omni, Amaron, Chemish, and Abinadom take minuscule amounts of text, leaving room for successive generations until Amaleki, who had no living children (Omni 1:25) and no way of conveying the plates to his only brother (Omni 1:30). Thus Amaleki had no more genealogy to preserve and more room left so he took the remainder of the space. All of this implies a physical object with limited space and a specific family situation.
We are often hard on Omni, Amaron, Chemish, and Abinadom, and sometimes even Jarom, for writing so little on the plates. We do not know their economic and technical situation and do not know if fashioning more plates was ever an option for them. They might have written more had they had the room, but they unselfishly saved some space for future generations until the line ended. Amaleki’s brief writings are definitely worth them saving the space.
Joseph Smith had a much less expensive and consequently more abundant writing surface to work with. He thus had no constraints if he were merely telling a story. If there were no physical constraints on the plates, there would have been no reason for the apocopated narrative.