What is going on with measures of programming language popularity?

Your first mistake is assuming that COBOL code was written in the 80s and untouched since then. People are still adding to COBOL code even today, and the language itself is still evolving (the newest COBOL spec was in 2014).

> That's where most code ends up getting written.

That's where most of the easy code to find and count gets written. But there is much more code that's outside of user-facing applications. Operating systems and drivers are relatively small, but have a much higher fraction of utilization since you're always using them. Embedded code is massive--not just the obvious things such as your car or airplanes, but also things like the microcontroller in your disk drive, the bluetooth controller for your headphones, your refrigerator, your microwave. There's the business applications: billing, payroll, corporate intranet, not to mention things such as scheduling the automated builds and tests or the management of releases for all of those applications. It's easy to forget that all of that stuff exists if you never work on it, and it's especially easy to think that it can't be that large.

If you avoid double-counting libraries (which is how I interpret the first number), then applications become a lot smaller because so much of applications is hooking together libraries. This is particularly true of non-app-y JS. By contrast, a lot of the business backend application logic (particularly for things such as payroll) is essentially 100% custom-implemented, so a much smaller fraction of it is common libraries. On pretty much any other metric of code use, though, such applications become far smaller in importance.

I'm in my 30's and one of the younger people in my department. I work in Engineering. I don't use Github I do not know anyone personally who uses it. I think it is probably a generational thing.

Search engine result as well I'd be suspicious of. If I am searching a programming language it is something I don't use very often thus why I am looking up the information. The languages I use the most often I have stack of books on my desk rarely need to look anything up with a search engine.

The big problem is all the major indexes are driven by search engine measures, and those themselves are highly sensitive to any change in the underlying search engine methodology itself. So a small change in Google's ranking algorithm will see a language move up or down dozens of places.

I would tend to focus more on job ads personally because those are at least linked to "real intent" to use a language for something tangible. You don't put it in an ad because something is controversial or had a lot of news lately etc. which can all lead to things being Googled a lot or getting a spurt of search activity.

Github's index is nice in that it is based on actual code, but then it's also heavily biased by what is open source and therefore doesn't fully reflect industry use of languages (which is why I think it deviates from other indexes to put Javascript and Python a bit higher, and less emphasis on say Java and C#).

Specifically, complexity will generate more questions than difficulty.

I dont think these measurements are any good or true reflection of a languages usage in the industry, some languages go totally under the radar, like clojure/clojurescript.