The first Rash"i in the Torah cites Rav Yitzchak's question as to why the Torah didn't begin with the first mitzvah, because it's assumed that the purpose of the Torah is as a mitzvah guide and not a history book.
However, what doesn't get answered is if we should assume that if there is a necessity to include historical figures, why not limit it to those that in some way influenced only Jewish people? In other words, should we assume that the Torah is meant to be a book for the Jewish people? (Not that we exclude Gentiles from learning the Torah if they wish, but it's main purpose is for Jews.) So, why do Jews need to know the family history of non-Jews such as Yishma'el and Esav?
I can see that at least regarding Esav's lineage, Amalek, might have some Jewish "significance" as eventually that nation attacked B'nai Yisra'el. But, if a non-Jew had no direct connection in any way with B'nai Yisra'el, why do we need to know the family lineage at all?