I sort of resemble that (OP) remark :)
And I sort of go otherwise out of the box.
I think folks tend to go with what they know until unless they have sufficient reason to change. What met requirements on initial system architecture is often a matter of when it was designed.
My original setup way back a long time ago was Linux (Debian) + Apache + PostgreSQL + PHP.
In the almost two decades since then there have been a number of alterations leading to currently: Linux (Debian) + (custom application framework + Apache + Redis) + Postgres-XL + C++.
Of course, without content, especially content others need/want, there is no requirement for the above. Content comes first, all else is 'merely' publication, distribution, and marketing.
My, mostly out of the WebmasterWorld box, interests include UXD, personalisation, contextual content delivery, direct affiliate pre-sell and ad space sales, API ad delivery, natural language programmed site search, internationalisation, unconventional marketing, apps, analytics, machine learning in all the previous...
Sadly most webdev fora are (1) hyping all things Google, (2) chasing the latest framework/programming fad, (3) pushing 5-10 year past best use by date SEO, (4) suggesting bland unimaginative SMM...
That WebmasterWorld suffers from (1) is no surprise, that it is far less prone to the others is a major reason I hang around despite the, imo, regrettable lack of folks with similar interests to mine.
Learning is, if not constant, certainly ongoing because webdev requirements and best practices are ever evolving and those who fail to adapt in a timely manner... this thread made me think of all that I've learned in the past 20 years to get up and going and to keep up and going; quite a list actually. Just not too many matching your examples.
I do take your point and you are correct but then no forum is strong in all areas. Actually no (public?) webdev forum is where cutting, let alone bleeding, edge webdev is discussed, not least because of the subsequent deafening silence. In a WP, shared host, Google-centric, cut-n-paste bubble the interests of the majority are narrow and capabilities limited. Finally, there are far more choices/options than back when; not necessarily better but certainly greater. Too many choices too often cause paralysis. And too little time. That especially.
I made a list of all the fora I'd like to see added but when then I looked at all the under-utilized fora already extant and I deleted. Just find the best fit and publish a post, if there is a sudden (unexpected continuing) level of response/interest I'm sure a more explicit forum would be created. Not that I'm holding my breath - most mobile posts are in the Google fora not the mobile; addiction and fixation are rampant.
But I do read the 'odd' posts that show what others have and are doing. I may not respond as an area outside my knowledge or usage but that doesn't mean that I'm not interested. iamlost not narrow! I hope. I know that I still post stuff that gets none to one replies; it's daunting but, as Marshall said: do not stop posting, someone will benefit. Even if you never know.