The Nephites in Zarahemla apparently felt that they could not kick Korihor out of Zarahemla, since the law (after all) said that a person could only be punished for committing an actual crime in violation of some written statute or law. But the people in Jershon had no trouble throwing him out of their new city and land. Why was that the case? The answer may tell us something about the law in the Land of Jershon.
The people of Jershon, the recently converted Lamanites, were certainly more righteous than some of those in the land of Zarahemla, and perhaps they may have had different laws there. Were they bound by the law of Mosiah? Perhaps not. They had their own city, given to them for their inheritance, so they may have been somewhat autonomous, operating under their own local rule. Having come from the land of Nephi where religious speech was only allowed by a royal proclamation (see Alma 23), these Ammonites may well have felt no need to give Korihor an open microphone. At least we know that Korihor had no recourse against them when they kicked him out.