I wouldn't say there aren't "any" such jobs. And there are a lot of languages I never look at ads for, so I can't say I have any sense of what their market is

I wouldn't say there aren't "any" such jobs. And there are a lot of languages I never look at ads for, so I can't say I have any sense of what their market is like. And of course there are whole domains (like C++) where the ecosystem is just intrinsically older. But by and large (and this gets back to the original article), once your core "keyword set" has gotten long enough in the tooth (which I'm pegging at an age of 5 year or so), the number of ballpark-open offerings (as in: you have enough XYZ that they're consider talking to you) does seem to drop quite precipitously. And the more "skinny pants" your domain is (like web stuff), the more this rule seems to hold. So the JS ecosystem would seem to be a bellweather example -- nearly every role seems to require either AngularJS or React (5 and 3 years out, respectively), or something similarly recent; pretty much no one is interested in jQuery or any of the older frameworks, these days (except, as the other commenter stated, for small maintenance projects).