I think part of it is that geniuses gets (or at least feels) rewarded whenever they try learning, while other people might not. For the same amount of effort, the amount of new knowledge gained by other people is fewer than what geniuses can get. Overtime, leaning no longer feels worth it. Thus normal people no longer feels curious while geniuses still do.
I thought of it from the other end. Curious folks end up engaging in cycles of formative learning that the less curious do not. The perceived intelligence follows. Its the process that makes the difference.
