The newly formed, and newly inclusive, nation of Nephi had lived the commandments for two hundred years. Therefore, they prospered. After two hundred years, they finally return to the problems of old. They became rich, and once they became rich they “were lifted up in pride,” and began wearing costly apparel, that harbinger of a people drifting away from the commandments.
The earlier egalitarianism was abandoned, and social hierarchies were becoming normal. Thus, “they did have their goods and their substance no more common among them.” It was what we would expect of a people who began to wear costly apparel.