1)
Why does it discuss the descendants of Elazar, but not of Itamar?
1.
Radak: Kohanim Gedolim come from Elazar forever. So Hashem told Pinchas when he was zealous for Hashem [and killed Zimri] - this was Bris Kehunas Olam. There were also Kohanim Gedolim from Itamar, e.g. Eli, Achimelech and his son Evyasar.
