The thing is Sanchez is guaranteed to get in to the Chile side so knows that his performances will not affect his position in the Chile side. There is no guarantees that if Arsenal dont sell him and he feels pissed off there is no guarantee that he will give everything of himself and indeed he could become a huge distraction and issue for team harmony. Indeed if he knows that he is coming to City for instance why would help Arsenal to get top 4 if it meant that City might miss out
I think him giving 100% is guaranteed, hes not a Costa type, he cares about his legacy. If he had a different attitude im sure we would have sold him.