That kind of stuff just takes a bit of time. It's kind of irrelevant to the language itself. Python and Ruby didn't hit the mainstream until the 2000's, despite being invented in the 90's. C# and Java both have huge company backing, and C and C++ have had traction since the 80's and earlier. And we all know sysadmins love Perl. Haskell's popularity is only a recent thing. It only kicked off with a few proper books in the past few years.
I wouldn't exactly call Haskell "popular". It isn't as obscure as some programming languages, but realistically, it sees comparatively little use in practice.
And Haskell predates Python, Ruby, JavaScript, Java and C#. It has had a very long time to become more widely used, yet we just haven't seen this happen. It's not like people don't know about it; many students, academics and practitioners have been exposed to it for years now, and it does get a fair amount of hype for a language that has experienced limited use in practice.
I just don't think it offers enough benefit for the cost involved with learning and using it. If the balance were better, we'd see it being used. But that isn't the case, so it sees minimal usage.
