Ancient cultures were so comedically wrong on so many things that I have a hard time finding this odd. they simply had no or almost no idea how many parts of the universe worked. Female genital mutilation is appalling but it's no more nonsensical than bleedings, taking mercury as a cure-all, or wasting decades of your life trying to transmute lead into gold.
There was a historical shift in beliefs.
I find this very odd. How could a major cultural lineage be wrong about something so much a part of ordinary experience?
When I say wrong, I don't necessarily mean that we're right, or the ancients were right, though there's a lot of evidence that the Victorians were wrong.
My favorite theory is that people's amount of desire for sex varies sufficiently that there's enough noise to make it easy to see patterns that aren't there. I leave the possibility open that there was a change (possibly dietary) which affected libido levels differently between men and women.
People are sufficiently punitive about sex that there's going to be lies and misdirection to support the current theory about how people are supposed to be.