As with the Nephites, the means to comparative wealth is trade with other locations.
Archaeology: Richard A. Diehl discusses the way in which the Olmec horizons became so influential:
What kinds of contacts created these horizons? Explanations put forth in the past include colonization, conquest, religious proselytization, and trade; of these, the last fits all the evidence much better than the others. By 1200 B.C. Olmec merchants penetrated highland and Pacific coastal Guatemala, Oaxaca, and central Mexico in their quest for obsidian, jade, serpentine, iron ores, basalt, cacao, salt, marine shells, animal pelts, and exotic bird feathers. Obsidian and basalt already circulated outside their immediate source areas; in these instances, the Olmecs apparently managed to insert themselves into the established networks and export the goods back to their home bases. In the case of iron ores, and perhaps other materials as well, they created demand for things that no one had used before and even colonized unoccupied source zones.
Local leaders must have quickly grasped the potential advantages of amicable ties with Olmec traders who could provide them with exotic goods embellished with motifs and symbols of rulership. Regular visits by Olmec merchants strengthened these ties to the point that some rulers adopted the outward trappings of Olmec elite culture and may even have accepted Olmec women as marriage partners. The intensity and duration of these highly personal relationships depended upon the fortunes of individual Olmec rulers and merchants and their foreign trading partners, and probably waxed and waned from one generation to the text.
Redaction: The phrase “that they might get gain” is almost certainly Moroni’s judgment, since his father used it frequently (and disapprovingly) in describing the influences that destroyed Nephite society. Its context here is similarly pejorative.