A common story goes:
Young children love asking ‘why’, and they often have an earnest curiosity about it that is rare in adults. Something about the process of growing up seems to cause that childlike curiosity to stagnate.
There’s a lot of compelling explanations about societal norms that actively stamp out that curiosity (i.e. school training kids to conform and regurgitate facts, parents subtly punishing kids for asking questions, etc). It seems likely to me that these are at least part of the story.
But it also wasn’t obvious that they were the whole story. I could easily imagine it also just being the case that small children are optimized for learning and older humans are optimized for doing and the brain automatically shifts away from it. [edit: or that this whole thing is imagined]
Are there any cross-cultural studies that do anything to check how this phenomenon varies, depending on upbringing?