Cultural: The casting out was not intended to be a simple relocation, but a punishment. By removing the people from their lands they removed them from their direct ability to provide for themselves. To the degree that they were also removed from a kin structure that had retained their lands, they were also deprived from anyone who would have been expected to have helped them. What happened in their removal to Jershon is that they were accepted into a new type of kinship bond, one that relied upon the gospel rather than kinship.
That new fictive kin relationship was the bond that provided the support for the newcomers than kin would have been expected to provide. This new fictive kin bond provided place and sustenance for the newcomers, which was clearly not the intent of those who had driven them out, therefore we read that the “Zoramites were angry with the people of Ammon who were in Jershon.” The Zoramites were angry because the people of Jershon had acted differently than expected, and had foiled the attempt to punish the dissenters from Zoramite religion with a banishment that might have been a death sentence for many. Therefore the Zoramite leader attempts to reinstate their punishment by having the people of Jershon expel the people so that the intended punishment could take effect.
Why would the leader of the Zoramites have assume that the people of Jershon might comply? The Zoramites were still part of the Nephite hegemony, even if a tenuous partner in it. A group of people had been expelled as social deviants, and for most ancient communities, those who threatened one city could be presumed to be a similar threat to other cities. The leader of the Zoramites was expecting the people Jershon to assume that those who were expelled were expelled for a reason that would also be threatening to the government of the land of Jershon. Of course the presence of Alma and his fellow missionaries allowed the leaders of the land of Jershon to know the nature of the dissention, and to understand that the very reason that they were expelled from the Zoramites would actually make them excellent members of the community in Jershon.