Unfortunately, Andy doesn't have the benefit, as Fed has by virtue of the number of tournaments he has played, of being able to duck out of a Masters here and there. As far as I am aware, Toronto is a mandatory tournament and if he hadn't played he would have been fined and carried a 0 point penalty for the rest of the year. It may well have been worth it in this case but I don't think it's in Andy's nature to shirk his responsibilities - he genuinely seems to play it by the book.
I did think Andy felt obligated. He was probably overwhelmed by the situation anyway. And then Lendl was waiting for him in Toronto.