To be fair, if I had a junior dev who couldn't skim a man page of 19 000 words, I would have freestanding concerns about their ability to contribute -- being able to inhale knowledge is a core competency of any engineer.

That said, I hear you when you say that most folks (think) they have better uses of their attention.

I daresay they're wrong, but it's not my place to dictate terms to anyone's curiosity, my own included!