A casual look at the math shows around 59% of the questions over a sample period are related to the broader project management field. Since frameworks like Scrum are valid project management methodologies, albeit with a shorter history than more traditional frameworks, the big surprise ought to be that there aren't more questions about these newer, complex, and often difficult-to-implement frameworks.
The solution, as I see it, is to leverage the baked-in tagging and filtering tools to enable domain experts and visitors to focus on the areas of project management of most interest to them. I talk about this in much greater detail below.
Agile is Not a Methodology
I won't belabor this, but it needs to be gotten out of the way. "Agile" is not a framework or a methodology. The Agile Manifesto is a set of principles that could (in theory, anyway) be applied to any framework that buys into its value system.
151 of 254 Questions Since June 2014 Aren't "Agile" Questions
There are currently 151 questions just since June of this year that are not tagged agile, scrum, or kanban. This means that questions about agility represent only around 40.6% of recent questions on the site.
You can run your own queries if you like, using:
created:2014-06-01..2015 is:question -[agile] -[scrum] -[kanban]
as a reasonable starting point. You'll have to sift through them if you want to quantify quality or some other criteria, but I find it hard to accept that PMSE is essentially an organ for any specific methodology given those figures.
Agility Isn't Only About Software
Even if we accept your major premise, Scrum, Kanban, and Lean aren't only about software delivery. I've personally used Scrum and Kanban on purely administrative projects, and Lean is commonly used in manufacturing. While Scrum tends to have a lot of mind-share in the software development space, it is certainly not limited to that, nor are the principles of the Agile Manifesto limited only to such commonly-referenced frameworks or applications.
Use Tags to Filter
I personally have very limited interest in the application of project management to the textile industry, or to abstruse questions about obscure Six-Sigma calculations, but that's what tags are for: to allow experts and visitors to quickly filter Q&A by topics of interest.
StackOverflow is a great example of this: I follow tags of interest (e.g. Ruby) while filtering out questions about C and Java. This allows the overall community to grow, while allowing people to ignore or avoid topics of no interest to them. I don't see why the same techniques shouldn't apply to PMSE.
Some Topics Generate More Questions and Answers
Again, setting aside the false premise of the preponderance of such questions, it's certainly true that some topics generate more questions, answers, or simply interest than others. Again using StackOverflow as an example:
- TCL has 563 followers and 3.1k questions
- C has 29.3k followers and 162.8k questions
- C# has 53.8k followers and 731.1k questions
I occasionally read/post in TCL, but ignore C and C#. By definition, my TCL posts get seen by fewer people, and I don't reap some of the extra rep that posters in higher-volume tags receive. On the other hand, the number of questions that I have to follow to stay abreast of the tag is much smaller, and I rather like that. By comparison to C#, the TCL tag is a bit of a language ghetto, but it also attracts some good questions and some undisputed experts in the language.
Participating in a low-volume tag is a choice that I am able to make freely. If volume were all that mattered, I'd participate in C# instead. Meanwhile, I think the system works well.
From a PMSE standpoint, if you feel that the new Electro-Convulsive Therapy Widget Delivery Methodology is where you want to read and post, you should feel free to do that. You may get less reputation from answering questions in a topical ghetto, or receive fewer answers from asking a question very few people are expert in or have an interest in reading about, but the platform still supports that choice, and the site mechanics of gamification are pretty transparent about the potential trade-offs.
On casual analysis, I don't believe the site actually skews strongly towards software delivery or agile methodologies. Even if it did, that would simply show that there are more questions (and possibly more varied answers) about these topics, as other topics might represent solved problems or have lower interest to site visitors.
Either way, I don't believe that any action is needed. I think the Project Management tent is big enough for all the methodologies represented here (and more besides), and while having visitors or experts in other methodologies would certainly add to the scope of the site, I certainly don't see the site's current scope as too narrow.