Sculptures Questions

why did the greek/roman artist make sculptures without pupils in their eyes?
I was in my HIstory class and we were looking at all the sculptures of ancient rome and greece. And we noticed that most if not all of the sculptures didn’t have pupils in their eyes. We were wondering why they didn’t, because it was a little creepy.
The statues were originally painted, so the pupils would have been drawn on.
http://io9.com/#!5616498/ultraviolet-light-reveals-how-ancient-greek-statues-really-looked