Yang Kai could teach relevant shamanic spells to a few others talented enough and willing to learn. But he likes to keep such knowledge to himself, despite going around asking for secret techniques to teach to the hundred thousand people he retrieved from his star field. Such selfishness is also demonstrated by the outrageous 30% levy he imposed on all the sects he beat into submission in the northern territory. Alas, this is xianxia, so the MC never gets a karmic response, even though every single other character does when doing a similar thing. It's the inherent weakness in this literature genre.