Xabi Alonso was a true professional during his five-year tenure with Real Madrid until the very end. But then, he decided to sign for Europe foes Bayern Munich, coached by Real Madrid archrival Pep Guardiola. And this is indeed a big difference. Had he signed back for Liverpool, for Schalke—like Raúl— or for Besiktas—like Guti— this would not be a huge deal. But he decided to join Bayern Munich, one of the clubs that will be competing against Real Madrid for Europan supremacy in the upcoming years. The team that knocked Real Madrid out of the Champions League two seasons ago while Manuel Neuer made fun of Sergio Ramos' missed penalty. It's fair to say that Bayern are "Europe's FC Barcelona" for Real Madrid. They are los blancos' biggest rivals.
In addition to that, Alonso is going to be coached by Pep Guardiola. Sure, he is a great coach and Alonso will learn a lot from him. But he's Real Madrid's public enemy number one, and that doesn't make it any easier for Real Madrid fans to forgive Xabi Alonso's departure.
But the worst thing is that Alonso's departure harmed Real Madrid's roster. The midfielder left with three days left on the transfer window and left the deep midfielder position for Illarra or Toni Kroos. The first has a lot to learn and is probably a bit green to be Real Madrid's undisputed starter for that position, while new signing Kroos is yet to adapt to that position, even though he's showing some promising signs.
Real Madrid should not have hold the door open for him. What if Ancelotti and his men play against Bayern Munich in the Champions League and the German club win with two huge games from Alonso? What would the board feel if that is what happens?
The media discourse is focusing mainly on how "honest and honored" Xabi Alonso was when he decided to leave Real Madrid because of a "lack of motivation after winning La Décima". If that was the main reason behind his determination, why didn't he leave right after lifting the trophy? Why didn't he leave after the World Cup? He had three months to make up his mind. One could think that Alonso might have felt that lack of motivation and desire during the pre-season stage in Los Ángeles.
But maybe he felt it after Javi Martínez, Rafinha and Thiago Alcántara got injured.