Isn't it a facet of productivity of the language that it's easier to write certain types of libraries in one language than another? If you're writing a compiler, the fact that lots of people write parser libraries in Haskell is a point in favor of Haskell, whether if you intend to use those libraries (because they're available and production-tested) or you intend to write your own (because it's demonstrably a productive language for that sort of work).