@dopeboykx
I think the logic behind making Yaa the tribe's chief is that she is a simpleton but also aware that the others are smarter than her, that she is not disliked by any of the tribe members and does not dislike any of the others.
So they knew that Yaa would listen to the advices from the experts and also accept a decision made by the majority of the tribe in important matters.
Any other member might have not listened in certain situations and pushed through with their own opinion instead of asking and listening to others.
Also there might be some mountain elves that view certain other tribe members as "rivals" and as such if those clan members become tribe chief they might ignore the opinions of those "rivals".
Or the other way around if someone they view as "rival" becomes tribe chief they would not fully / honestly support that tribe member who becomes the tribe chief.
Hence making the simple-minded Yaa the tribe chief might have been judged to be the best option for the tribe.