Rashi: It is telling us that, when Eisav saw how Ya?akov carried out his father's instructions, and went to Charan to avoid marrying a daughter of Cana'an, he put on a pretense of fulfilling the wishes of his father by marrying a daughter of Yishmael, but without divorcing his wicked Cana'ani wives.

Rashbam: When he saw that his father had conferred upon Ya?akov the B?rachos of Avraham, and that he instructed Ya?akov to marry a woman from his family and not from Cana'an, he figured that he lost the B?rachos because he had married a Cana'ani woman, and that, perhaps, by marrying a daughter of Yishmael, he may regain part of the inheritance that he had lost. ¹