In the case where an article causes you to subscribe, the topic area can be sustained by a smaller audience.

Eg., this is how netflix maintains a large library of niche films. It is enough just that they profit on them, not that they are popular.

The issue in OP appears to be that his articles were always included with the printed newspaper, and some people were curious enough to read it. However those people would never think to seek out that content.

So it's a question of "how do you serve the intellectual curiosity" in an era where mere popularity is the main recommendation system?

I don't think it's as big of a problem as he seems to think, only, that newspapers now have no answer to it. Many institutions for the intellectually curious (newspapers, universities, etc.) don't serve that function anymore.