From what what I know about non-fic writers in real life--which is only a handful--their craft centers around their knowledge, and not so much their writing skills (someone who has a ph.d in psychology most likely can put words together well enough). So they aren't spending their time on a writers forum. Their loss, though. Forum is wonderful for many things!
Plenty of non-fiction writers are skilled both in their area of expertise and in their ability to write about that area in an engaging and informative way. Among them are people with PhDs who can put words together in a better than 'well enough' fashion.
Back in the day, before the Internet went public, I used dial-up to a Compuserve forum filled with writers
and editors. Other than peer review, we never really discussed the craft of
writing though.
I think one reason is because we were not working on our own without support. Given non-fiction ideas and expertise and some basic writing ability, there were professional copy editors etc. who would help get the article into shape.
And things like “show vs tell” simply were not applicable. Does a phrase need to be beautiful and elegant? Not so much — plain is best, giving just the facts in an easy-to-understand way.
Look at the type of writing skill that we don’t see discussed here: how to write a grammatically correct sentence. How to write a paragraph with topic and supporting sentences and make paragraphs cohesive rather than just arbitrary breaks in a wall of text. Are there any threads about pronouns and clear antecedents? I did see one about being understood by a global audience re non-universal terms and idioms.
In non-fiction there is no characters to invent, flesh out, and develop over a story arc. There is no dialog. There is no plot like in fiction, but there is an outline regarding presentation order when explaining something. The choices there are pretty objective though, not artistic. The standard forms of various types of essays are taught in school.
So, almost all the threads I see here are for things that don’t apply to non-fiction.