While I understand this at some level, I also feel that Zidane is shying away from an important aspect of being a football manager - rebuilding a squad. He has now proved that he is able to manage a squad, field a team, set the tactics, handle the personalities and win games etc., but he is leaving right at the time that the squad needs a major overhaul.
People talk about him leaving at the top, but the real challenge would be to reach that top again with a new team - SAF style. Perhaps Madrid is not the club to do this at, but you would think he would have bought himself some transition time with three Champions League titles.