This is a great question.
First, Greece was mountainous. Mountains cover about 75% of Greece. These mountains are not particularly high but they did a good job of separating the Greeks from each other. This was, undoubtedly, a contributing factor for the vast number of Greek cities and the lack of a formation of a centralized Greek state.
Second, what also contributed to the rise of the city states was the lack of a great river system. A glance at other ancient civilizations shows that a great river system usually leads to a unified centralized government, such as in Mesopotamia (Euphrates and Tigris rivers), Egypt (Nile river), and China (the Yellow river).
Third, Greece was divided by a sea. And on this sea are many islands. This point, too, created more independent city states.
Based on these points, it was only natural for Greece to have city states that were separate from each other.
As for way of life, Greeks were traders and seafaring. This, too, makes sense, because they lacked natural resources. So, they needed to travel abroad to get what they needed.