Maybe because he was BY FAR the best player for the same group of kids two years ago at the WJC. Maybe because he faced the second most shots, on a bad team defensively and yet still had the second highest sv % in the Q.
Also he is by far the strongest goaltender technically. That first goal was bad but he hadn't faced a shot for four months before that. After that the Russians had several good scoring chances and Mason made them look routine. He's always in great position.
The fact he's not playing tonight pretty much shows what Craig Button was talking about. Hockey Canada knows what they have in Mason and they want to get another look at the other two guys.