It is impossible to understand that Yitzchok and Rivka should have favoritism with their children. For sure they loved with a Cheshbon to give love to whom it’s needed. I remember a famous Adam Gadol who had a large family, and I always saw him walking and holding hands with a family member who needed the most Chizuk. You don’t love whom you happen to like, you love the one who needs your love!
I don’t even dream to truly understand these people. But we can say (at least: בְדֶרֶךְ רֶמֶז as a Remez) a reason why Yitzchok loved Eisav. First of all, right after it says how Yitzchok and Rivka had aggravation from Eisav’s wicked wives, we have Yitzchok calling Eisav in order to give him the Brachos. We see that Yitzchok knew quite well what “his” Eisav was all about, and when he loved him and wanted him to get the Brachos, it was in order to be M'karev him.
Notice how the entire relationship between Yitzchok and Eisav was centered around food. The ongoing: וַיֶאֱהַב יִצְחָק אֶת עֵשָו כִּי צַיִּד בְפִיו love of Yitzchok for Eisav because he enjoyed his food (Rashi quoting Onkelos), and now by the Brachos, Yitzchok is asking Eisav to make him good food. The Gemara says that in order to have Nevua, a person must be B’simcha. Like by Elisha, who was depressed after Eliyahu left him, and so he said: קְחוּ לִי מְנַגֵן מ"ב ג טו “Bring me a musician!” to give him Simcha. And the Meforshim compare the Simcha of a: מְנַגֵן musician to the Simcha of Yitzchok getting good food from Eisav.
