'Rashi': It is for the same reason that the Torah lists them - [to teach that] amidst [Hashem's ¹ ] love of Yitzchak, He gave to his son ² Esav an inheritance of these chiefs.

Malbim: Because Bnei Esav destroyed and dispossessed Bnei Se'ir, and became chiefs in place of them, it tells how many chiefs were of Se'ir. There were 13 Bnei Yishmael, 13 Bnei Keturah, 16 Bnei Esav (all agree that Timna is not counted) and 26 Alufei Bnei Esav in place of 26 Alufei Bnei Se'ir. In all, this is 68. With Amon and Mo'av, which were also from Avraham's family, there are 70. Just like there are 70 nations in the world, 70 princes and chiefs came from Avraham's seed ³ , and correspondingly 70 Nefashos from Bnei Yakov, who are the root of Yisrael, like the Ari Zal wrote in Sefer ha'Gilgulim. This (Yisrael) is opposite this (the nations)!