What Alma and his brethren had taught in Antionum was contrary to, and totally incompatible with, the teachings of the Zoramites. Therefore, when the Zoramites learn of those who had been converted to the Nephite religion, they did not attempt to integrate them into their society, but rather cast them out.
When the converts from the land of Antionum were cast out, they went to the next nearest Nephite land, which was Jershon. Jershon was the land where the Ammonites had settled. The Ammonites were the former Anti-Nephi-Lehies who had covenanted not to bear arms. Thus, this land that did not have its own natural protecting army accepted immigrants who needed to be integrated into their populations and given land to improve and cultivate. What is even more important is that it is the land Jershon, which is next to the land of Antionum. That fact becomes critical in the next events.