These are a rather interesting articles:
How Early Academic Training Retards Intellectual Development
Early Academic Training Produces Long-Term Harm
They make a good point basically about developing motivation before formal training.
And a second supporting reason could be the raw development of the basic mental and physical skills that make learning easier.
Like fine motor skills make writing less a chore, so finer reasoning skills through exposure to ideas and supporting concepts, makes more formal education more productive.
The world is a fascinating place, and often the story is drained out from around the facts.
– History can be told naturally as lots of stories, rather than just dates and places
– Science explains how the universe works, near and far, with many fascinating natural machines and processes
– Mathematics allows us to be specific about our world and gain a deeper understanding how things work
– language and speech are ways of communicating stories, and if someone is exposed to quality books and conversations, a lot will just fall into place, and things like grammar will just make sense naturally
– music is a special language all of its own, with it’s own history, infused with emotion and intellect
Teaching about this history of a discipline can be an effective way to teach about that particular subject.
To show how through time, things were developed, and new applications discovered, as part of a larger narrative. Humans need human motivation and context; learning can be fun of course, but nothing is purely for its own sake. Even learning theory for the mental challenge, solving puzzles, and the thrill of discovery, is a human purpose.
Without a strong, and even insatiable curiosity to understand how things work, and the desire to seek deeper experiences, learning is harder, and can just produce drudgery and unpleasantness.
Many teachers can contribute to this by the way they teach; and may lack a vibrant learning vision themselves.
A purpose and narrative based education that never strays far from application will be much more interesting and digestible. Learning should inspire the learner to achieve even more, and feed the appetite of curiosity once it dawns on them what kinds of things they can actually do, and understand with that knowledge.