To help remedy that, here’s my recent post on system administrator site documentation with docbook, and a few “intro to docbook” links that were helpful to me.

Nice thoughts.
I agree completely.
Your last reason is very important. People, many times, do not share knowledge, due to insecurity. Sounds funny, but it is a fact. They (probably) get “married” to the company and whenever they are acknowledged as S.P.O.C. (Single Point-Of-Contact), it soothes their ego.
Such people will do everything they can, to sabotage any plans to prepare / update documents.

In my experience, setting up a successful system, either complex or simple, requires a systematic approach from the start. And, which cannot be said enough, simplicity!

A database needs to be adjusted as little as possible. Sourcecode needs to be version controlled, Even in very small simple environments. Production environments need software releases, explicitly tagged from the version control. Not a few files to be fiddled with in order to make it work again.

Happy easter!