No one knows why these humans exist,but there are some theories,
one being that there was once a whole nation of humans that lived in caves.As the time passed they were suppressed to live deeper in the caves by predators and other civilizations that wantes to exploit their resources.
Over hundreds of years this led to them adapting to the dark surroundings and becoming what we see here.
Today these humans are almost extinct,and it is believed that there is only a hand full of them left on earth.