Or HaChaim on Genesis 25:28/אור החיים על בראשית כ״ה:כ״ח

1 ויאהב יצחק את עשו, And Isaac loved Esau. According to the Midrash Tanchuma Esau snared the love of his father by misrepresenting his true character such as enquiring about the correct manner of tithing salt. He did not bother to engage in such trickery except when dealing with his father. This was because he was not concerned about the performance of good deeds but only wanted to ensure his father would have no reason to curse him. He also hoped to obtain blessings. His mother could not dispense either, therefore he made no effort to camouflage his true self when in his mother's presence. This is why we find later on (27,41) that Esau waited for the death of his father before killing Jacob, whereas he did not wait for his mother to die before committing murder. The reason Rebeccah did not inform Isaac of Esau's wickedness may have been that Esau was careful never to put on such a charade in her presence so as not to give his mother an excuse to challenge Isaac's love for him. According to Onkelos who renders the words כי ציד בפיו as ארי מצידה הוי אכיל, "that Isaac ate from the game Esau hunted," we must ask why this reason did not also cause Rebeccah to love Esau, for surely they took most of their meals together or at least Esau did not discriminate against her? Perhaps the reason is that in accordance with the commentary of the Maharik on Even Ha-ezer 70,1 Isaac was under an obligation to feed his wife a meat diet. When a wife comes from a family who is used to such a diet the husband must keep her in the style she was accustomed to. Bethuel was a wealthy and influential man in his town, and no doubt Rebeccah had been used to a high standard of living prior to her marriage. She would not therefore be particularly grateful for the venison, considering it merely as her due.