That has been exactly my experience as well. There exist job places where "the requirements is in his head" is considered normal and in order and there is too much respect given to such "job security" selfish aes who never share things voluntarily.

As contrast, at an earlier work place there were "mentors" introducing newcomers to the domain holding introductory crash courses and doing code reviews. I understand why so many job posts here in Sweden stress the importance of knowledge sharing for common (not individual) success. Sharing knowledge means that more people can share the burden - not the other way around.