Because a lot of people think evolution was only as old as Darwin.
Some of those ideas may have gone back much further than even the 3rd-1st century CE. The alleged Phonecian creation story from around the time of the Trojan war was about how life began as senseless round creatures that emerged from mud and eventually over time became watchers of the sky.
And the Greeks credited their ideas around atomism not to Democritus but to the Phonecian Mochus of Sidon from around the time of the Trojan war.
But because any sources from back then haven’t survived, we tend to credit it to the later sources we can reasonably back up.
Yet the only reason we know that these ideas were around in the 1st century BCE is because the secretary of the Pope right before the Renaissance went around to monasteries bribing guards to smuggle out texts. The only copy of the book about evolution from antiquity was being eaten by worms before it was saved (there’s a Pulitzer winning book about its rediscovery and influence on the scientific revolution during the Renaissance called The Swerve).
But most people today have no idea that these ideas go back that far.
And I think that’s a shame.
Evolution is kind of a big deal and pretty relevant to our lives.
And the masses collectively forgetting those that came earlier on is a bit like those maggots having been successful in eating away at the legacy of history. Or more accurately, like the church having been successful in denying humanity its own history of innovation and brilliance, let alone having successfully suppressed that knowledge for over a millennia.