Can you give some examples?

I cant speak for the battles you mentioned, but the idea I got from recently reading Goldsworthy's The Fall of Carthage is that ancient battle was prolonged and in some senses rather timid affair. During the actual hand to hand engagement very few of the combatants were actually killed. Most casualties occurred in pursuit when one side broke and run. Therefore its not surprising that the most bloody battles were the ones where defeated army couldn't run, e.g., Roman defeats at Cannae and Trasimene where Romans got themselves surrounded.

So one might think that in your examples the low casualties are explainable by lazy pursuit.

For antiquity it has to do with the way that hopilite formations worked. They are great big masses of men often ten deep that work well against other hopilite formations and the unruly mass of "Barbarian" troops that fight individually. The men in the back push forward in formation while the men at the front are well protected by shields and armour and try to stab the other guys with their spears. Note that the men behind the first three rows or so are protected. The nightmare with a hopilite army is of course being flanked by cavalry. Another thing about hopilite formations is that they are very slow to move and not very maneuverable. This means that the losing side can break and flee relatively easily. The winners have a choice of either breaking formation themselves to chase, which risks the enemy reforming quickly and counterattacking while they themselves are out of formation or letting the fleeing enemy go. This is how we get stats like those of Marathon where the Athenians lost 192 men according to Herototus and Potidaea during the Peloponnesian war where the the victorious Athenians lost 150 of 3000.

Oswyn Murray: Early Greece