What influenced the decision to live in Greece is that there was arable land there and people tend to live everywhere where it is possible to make a living. In other words, people live practically everywhere that they can and Greece is a place where people can live. Therefore, people decided to settle in Greece.
This question seems to imply that people only live in the most hospitable of locations. This is simply not the case and it was not the case even in ancient times when the population of the Earth was so much smaller. Think about some of the places that have long been populated. The Arctic has long been populated by the Inuit and others. Tiny atolls in the Pacific, like those of the Marshall Islands, have been inhabited for millennia. These are places where it is not easy to scratch out a living and yet people have lived there for a very long time.
What this should tell us is that people will live everywhere where it is possible to live. Greece is not a place where it is hard to live. Its climate was good for growing things and, while it was mountainous, there was plenty of land that could be cultivated. The sea was also a source of food. Because of these factors, we should not be surprised about the fact that people chose to live in Greece.