Mbappe egoistic attitude is the strongest factor. He will experience a decline in performance he considers himself an important player at the club that other players must respect, this condition is certainly not good for the team and also for Mbappe himself. Humble attitude needs to be prioritized, he cannot play alone without the support of other players, when other players boycott Mbappe by not giving him assists, he will have difficulty scoring goals and improving his performance.
For this reason alone, Ancelotti may be reluctant to include Mbappe in the squad. Mbappe is capable of scoring a lot of goals and his fitness is very good. But his behavior is completely different from Real Madrid players. Real Madrid is a strong team as a team. Real Madrid's good results are due to the contribution of almost every player in the team. Ancelotti will certainly not want to rely solely on Mbappe to shape his strategy. Mbappe's main problem is his unwillingness to assist. He just wants to score.
Even though it looks selfish in terms of every match, I think it's fine to rely on Kylian Mbappe because he can indeed be superior to other players with very strong performance and the tactics that are always used are very precise.
But I understand that Ancelotti is thinking again about getting Kylian Mbappe because of fears he will change strategy which will end in conflict with other players at his own club.
Kylian Mbappe is indeed a very talented player but I don't like it when he is too arrogant like he wants to excel himself.