I think personally the reason why he does not want to let go of Carr is because of that Carr was the first one chosen in the draft. It has sentimental value to him. Its kinda like owning your first car and not want to let go of it because it was your first car. Its broken and you just want to make all the repair necessary to get that thing running. But in the end it still just wont start for you. Mcnair needs to let it go and move on ahead to better his team.