The Ammonihahites were originally on the same standing as the Nephites. They were part of the Nephite politico-religious sphere, and had the opportunity to receive these blessings of the true priesthood. However, those blessings were only given to those who would not harden their hearts, and Ammonihah has done so. Alma continues to link true priesthood through the Son, or the Atoning Messiah, in whom the Ammonihahites do not believe.