It's probably because I recently read Akata Warrior by Nnedi Okorafor, but at first I thought the (to me) African-American sounding voicing of some of the characters (very noticable in the audiobook, but I think some of it is in the writing too) was making points about those characters. After listening a bit more I think the point is that there is no point, this is just how (some) people talk.