Your basic assumption about how myth-making happens is flawed. Myths aren't muttered into being by a random person "just making stuff up." No bearded shepherd sat down on a rock on Mount Olympos in the middle of the "Greek Dark Age" and decided to canonize the Olympian gods there on the spot. Myths are the product of many voices over an extended time period, both highly localized and also, at the same time, highly dependent on extra-local influence. Most mythology is the result of human beings attempting to understand the world around them and frame its phenomena in terms of human experience. Many of the most famous ancient myths were aetiological -- that is, their core message endeavored to explain some weather pattern, or unusual geographic feature, or the like. Dowden, talking about Greek myths, writes that they "are a way of thinking about the world around us and the people in it. It is in the nature of the worship of the Greek gods to generate myths, and it is in the nature of poets . . . to collect them and synthesize them into a compromise set of stories that develop shared ideas of what the gods are like and how they behave" ("Olympian Gods, Olympian Pantheon" in Companion to Greek Religion, Blackwell 2007). The Greek system that emerged in the early Iron Age was unusually productive at generating myths for two reasons. 1) Greek belief was heavily anthropomorphic, and gods that are like us are free to behave like us in all the ways we behave, good or bad. The fodder for myth-making is therefore very rich due to the basic nature of the deities in question. Compare this to other world belief systems that are much more aniconic--that is, non-representational. Of course it is still possible to make myths about gods that are stones, or rivers, but their repertoire of action is both more limited and less informed compared to anthropomorphic gods. 2) Greek religion was highly localized. This meant that "Athena" meant different things to different Greek enclaves, even at places that were only separated by a few miles. Each place cultivated their own myths about the gods they chose to observe, while at the same time regularly interfacing with the myths and protomyths of their neighbors. The result is a wonderful, chaotic hodgepodge of myths about a huge variety of deities and variations of deities.