You make a good point about posters with a wider range of experience of hifi in say retailing. There’s nothing to stop anyone putting these things in the system details or comments if they wish.
Nevertheless, it is extremely helpful to know how posters are listening to music. It’s not so such a matter of credibility as being useful to know where they are coming from. It is very interesting to know how combinations of gear are put together in practice.
Yet, there is an element of showing you've got some skin the game. We can see that from threads such as What's your commitment to vinyl. I guess if you're wanting your views to be taken seriously, people are entitled to ask.
One of the biggest music and hifi forums insists posters declare their own systems, if they are going to comment on sound quality.
I find it frustrating that some members make pertinent contributions in discussions, yet I can’t relate it to a real system. Sometimes, people talk about an item of gear they own, but we have little idea of the context in which it is being used.
From my own point of view, documenting my system gives me a greater understanding of it and how it might develop in future. How can others help me in this, if I don’t give them full information?