The Medrash says that Eisav figured out that there is no Din since even Avraham Avinu died.
There are three levels here. First he did Avoda Zara privately. Then, on the day of the Petira, even before he knew it, he had murdered someone and commited Arayos. This is public and would be shameful to Avraham Avinu. After hearing of the Petira he jumped ship completely, as Chazal say, he was Kofer in Techiyas Hameisim.