Because if Kai were to invest fully in someone, his first option was either his family or Uncle Liam's family.
Although he knew Cedric's personality in his previous life and he would definitely look after his family if something were to happen to him, he couldn't risk it because something might change with Cedric in this second life since even the timeline was messed up.
Let alone the fact that they were not blood-related. That's why Kai thought that he had invested enough in Cedric and it was time to help his family to become stronger, at least strong enough to be able to survive confidently in the current chaotic situation.
As for the Yellow Scroll, even though a Yellow Scroll could give him a 5th Echelon Rank Skill, Kai wasn't that interested because he already had enough skills that he didn't think another skill at the 5th Echelon Rank Skill would make any difference.
Besides, the skill was also going to be random, so Kai didn't really fancy it as much.
