But why? We don't even have a unified global idea of masculinity today, nevermind the span of history.

Why is it that middle eastern cultures see men holding hands to demonstrate platonic affection, whereas the same act would be distinctly unmasculine in most western cultures?

Why do most modern western cultures view weeping as distinctly unmasculine, but in ancient Greece it was considered unmasculine to not weep when faced with sorrow?

If different cultures, across different time periods, can see masculinity recognized and performed in different ways, then is it not clear that there is a separation between sex and gender?