I would guess that there are numerous reasons for people not posting their systems.
1. Laziness.
2. Don’t feel there is a need to do so.
3. Don’t know how to.
4. Feel self conscious about their system because it didn’t cost six figures like many systems on here.
5. Many people don’t want to make their personal situation public for a variety of reasons.
That being said, there are certain people on this site that I would love to see what they listen to.