Some of these colonies started as trade posts that expanded over the centuries, but many were sponsored and planned from an originating Greek city. If this was the case, what would be the factors that would motivate potential colonists to become new citizens of these founded cities.
In the case of the thirteen colonies, most of the founding populations came from either political (and religious) dissension in the New England region or those wanting to make their riches in the colonies in the Chesapeake Bay region. Are these the same motivations that would move Archaic populations around the Mediterranean 2000 years earlier?
As usual, the main people motivated to move away were the "surplus" people who found no place for themselves in their home cities. Younger sons of farmers with little prospects to inherit a significant plot of land, young artisans (or apprentices) who found the market too competitive or too closed to make a living. And so on. A different category were merchants who settled in distant emporia or colonies to trade.