Because they had an ideal of arete-basically the Greek standards of excellence that included, but was not restricted to, rhetorical skill, looks, battle valour, and cunning (think Odysseus). The amount of arete you had translated into time (ti-mey), honor,esteem, or dignity among your fellow Greeks.
Here is the part where you see the "all the way attitude" among the Greeks. The goal is to have the most time. It is a zero-sum game; it is just not acceptable to have ALMOST the most time, as there can only be one clear victor who has amassed the greatest amount of time through his arete. So, you see people struggling to attain the most arete by engaging in heated political debates, or going crazy on the battlefield, exc/
Note that these concepts were not only restricted to humans, but to cities. These ideals could be said to have fueled the tension between Athens and Sparta over which city would be the greatest hegemon, leading to the Peloponnesian Wars.
I wouldn't say that moderation was non-existant-it was particularly encouraged among philosophers under the guise of the "golden mean", the middle path..
Peace
