Well, the knowledge was available – the classics were taught in Byzantium and surrounding area like Persia alike, for 10 centuries after the fall of western Rome, while Europe/Italy was kinda floundering.
But the Council of Florence, otherwise a failure in its purpose (the Pope wasn’t recognized in the Eastern Churches and, well, he wanted to be) – nevertheless brought https://en.wikipedia.org/wiki/Gemistus_Pletho who was brought in from the Byzantine East to give them Western Romans some learnin’ and brought back all of the classics that had been missing in Western education.
Had it not been for the Fall of Constantiple a few years later, things might have been different but since things happened as they did, here was the West with this “new knowledge” (new to them), and off sprung the humanist movements etc all leading to today.
Had Plato + Aristotle been a part of the continuous history of the Western Roman empire, concepts like telegony + elementary particles might have continued.
But with suppression of knowledge after 1453 in the areas of Eastern Christendom with the rise of the new form of Islam (which was more “by the book” and distinct from the Islam that was around before, which was a more organic religion), Europe was untethered to history, left only with the books.
So, it took a while for concepts to “come back” again for them.