Well you have to understand that Morata begun his professional career in Real, I think he spent a couple of seasons playing for the youth teams as well. So he would take any chance to play for the club he loves. But I think you are wrong that he wanted to leave Juve. Juve never owned the player. Morata was loaned out to Juventus for two seasons and they had a fixed buy-back option on him which was activated in the 2nd season. He has always said that he was very happy at Juventus but if there is a possibility that he joins the team he loves, he will take it.
I understand that. I saw it in his eyes when he scored a goal against Real a few years ago in the CL 1/2 Finals, there was not much joy there.