Earlier quoted context omitted.
Almost every instance of this I've come across can be described by repeated localized, short-term optimization. No one ever sat down and said "How can I design a terrible system that's a pain in the ass to work with and unable to be extended?" Everyone sat down and said "How can I make that one thing that's actually my job faster?"
sometimes people also sit down and ask "how can I build a platform to do this kind of thing so expanding and maintaining that platform can be my new job here?"
Never ascribe to malice, that which can be described by laziness, etc.
It seems like it would take more work to specifically design a system to ensure job security than to just haphazardly design without coherent architecture, and consequently be the only one who understands it.