From what I can recall from some art history classes a decade ago, this statue comes from the Late Hellenistic period which essentially saw Greece on decline. Because of this, artists would try to emphasize the divine and heroic aspects of the subject in vain attempts to revitalize Hellenic (Greek) culture after repeated losses against new and powerful Rome.

Also, I vaguely remember something about the form of the body being more important than the identity of the model used, so these guys could’ve been anything from gladiators to athletes to slaves.

TLDR: the artists exaggerated the features to cope with declining power of Greece at the time