In the colossal head of constantine, why did the sculptor make the face appear emotionless and mask-like?

The sculptor was following a Roman tradition at the time to portray emperors as other-worldly, almost godlike beings. He makes his eyes very large and his face stoic to convey that he his someone not quite human like the rest of us, and perhaps he is above the fleeting emotions that govern the rest of mankind. 

What i think is that it adds loudness for preachers/church choirs. it is also able to hold up a lot of weight without pillars. : )) idek tho