Verse 9 is interesting. It mentions that Nephi, the father of Nephi, did not return to Zarahemla. Mormon told of his disappearance in terms that appeared to assume that he had died in 3 Nephi 1:3. Now Mormon simply mentions in passing, and over a decade later, that he still had not returned. Why mention Nephi, son of Helaman, when it is Nephi, son of Nephi, who has the records?
Mormon says very little of Nephi, son of Nephi. His story is coming later. At this point, Mormon is setting up the events that will destroy the Nephite nation, as reported in 3 Nephi 7. By mentioning that Nephi, son of Helaman, does not return, Mormon symbolically notes that true repentance and true Nephite religion, such as that which Nephi embodied, did not return.
What they got instead was a continued increase in the influence of the Gadianton robbers. They were so prevalent that both Lamanites and Nephites took up arms against them. Also important in this statement is Mormon’s separation of the Gadiantons from both the Nephites and the Lamanites. Mormon considers them a third entity, even though some of the members of the Gadiantons were formerly part of either the Nephites or the Lamanites.