[thinkpad20]

Haskell as we know it now, with high performance, large library selection, more powerful type system, advanced tooling, testing and profiling etc, has been around for significantly less time than that.

I also think that's a specious argument. Many things influence a language's popularity that have nothing to do with the language's actual value. Haskell is very idiosyncratic compared to other mainstream languages, requiring a "relearning" of a lot of skills developers take for granted. Many people balk at the learning curve and never get into it. Haskell has also received comparatively little contributions from industry and was never the pet language of a major organization (like e.g. C#, Java, Go, Rust, Dart, etc). Also the influence of Haskell can be seen in a variety of areas, from other languages adopting more advanced type systems, type classes, systems like LINQ in C#, and the increasing popularity of functional programming in general. Finally, although popularity drives language ecosystem and therefore usability, Haskell's merits purely as a language stand on its own regardless of how many people use it.