We have countless written records and ancient plays depicting Hellenic religion including myths and practices, but every myth has many versions with notable substitutions for characters, events, and outcomes including debated lineage of gods (Aphrodite, for example, has 2 main origins; being both of Ouranos' castrated testicles in Hesiod's Theogony but in Homer's Iliad she's the daughter of Zeus and Dione). While I can understand how a society that has no writing, like the Celts, having an extremely varied mythology how did the Greeks never formalize their myths into a single cohesive canon?
As an extension, while the Greeks were a collection of disparate city states why did the Romans never solidify their mythology into a single canon? Why is there no Hellenic equivalent of a Bible?
EDIT: I suppose this could apply to lots of cultures that had writing and inconsistent mythologies, but I'm most familiar with Greek/Roman myths
Source: reddit post