I'm honestly not sure what their justification is and I doubt anything they argue for it would really hold water. Either homage to the silent protagonist or purposely a blank slate you can project onto. As someone else said he barely emotes anything until toward the end of the game when some serious choices need to start being made. I got the impression they intended it to just be a reward for beating the game. But I think everyone would have preferred it be available from the start of left out completely