>>33632914This is nothing new for JRPGs. Silent protagonists, especially in 3D JRPGs, often have a single facial expression for most of the game, but during certain animated cutscenes, they show a different expression. In SM, it happens to be a smile that is the default, and it changes in some cutscenes. In others, like Dragon Quest 9 for example, you have :| face for most part.
In that sense, it is a deliberate decision. They leave the emotions up to the player's imagination, just like how they leave the dialogue out as well.