How up to new ideas a human brain is, how willing is it to learn new things, or gain the pleasure of knowing.
Kids are curious. Adults don't get less curious. It's just that the education system, or sometimes even parents do not answer their curiosity. The Internet is actually a good place. Because kids can get answers there. Examination system ruins it even further by grading on a subset of knowledge and kills creativity. Yes, learned helplessness. Less Will to learn. It is a sadness.
It could be due to Darwinism: Where trying things like new experiences or, heck, rebelling against school authority would most likely backfire. So the human brain plays it safe.
As ideas get stronger, less open to new ideas, for instance strong beliefs like religion already formed so more resistant to external influences. It is a problem when external people are used to judge curiosity in experiments, not the participant themselves! Additionally, more and more information online will be repeats of what the person already knows, so he or she will have to delve deeper to know more.