Imagine training a chihuahua to do tricks, then looking at an untrained golden retriever, not even try to teach them, and saying “why are chihuahuas so much smarter than golden retrievers?”
Of course modern writing/drawing utensils are on an entirely different level and paper was very expensive back then e.g. an average labourer supposedly only made enough per day to purchase less than 100 sheets, so practising was expensive.
No one said dogs, either, they said schoolchildren. It’s an analogy. Either way, it makes zero difference to the point. You could change my word to “skilled” and it would work the same. Skills are learned and thought, that’s what matters.
> A perfectly legitimate answer to that question might be that we stopped teaching them.
Which is what I wrote as the first sentence. The second is merely an analogy to exemplify that notion.