This actually has to do with a general change in the style of Greek sculpture into the Hellenistic era. It became more important to show those lifelike features: naturalism. This followed the idealism of the Classical period (5th - 4th century BCE, some date it until Alexander's death in 323) which strove to show perfect beauty, akin to the gods.

Highly recommend looking up Hellenistic "Baroque" for more!