The parent commenter said "learning about computers". Most "professional developers" don't learn about computers, they learn enough react to get a paycheck, but don't have an insatiable curiosity about how the whole computer works (i.e. the "hacker spirit").

Professional developers are not what this thread is about. It's about curious kids, about hackers, and that group does peek at kernel source code (as well as everything else).

It's something you never need to look at, until suddenly you do and then it's invaluable. Any time you format some data for another system and get a cryptic error code back, looking at the source code becomes invaluable.