There certainly are other factors than a language's productivity. I don't dispute that at all, or I wouldn't be writing so much code in C++.

But I think language popularity has very little to do with productivity or any other rational factor. Languages mostly piggyback on platforms that emerge rapidly at some point in history.

C came with Unix. JavaScript and Java came with Web browsers. SQL came with relational databases. Objective-C became widely used (if not poplar) with the iPhone. PHP came preinstalled with shared web hosting. C# comes with Windows. VBA comes with Office, etc.

Developers mostly just choose platforms not languages. Whoever makes the platform decides on the language and it will be "popular" regardless of how atrocious it may be.

And by the way, PG is building something today and he's building it in a Lisp dialect (http://paulgraham.com/arc.html)