Most of the programmers do programming for a living. They are not passionate programmers who like to learn new languages. They care about getting things done. Since Java, C#, Python, JavaScript, Ruby and Rails, PHP are all popular and have huge library ecosystem around them, for most of the 9 to 5 programmers, there is little incentive learn any functional language.
Also since all popular and dominant languages are either Object Oriented and/or Imperative, functional programming concepts seem too alien.
Even though I consider myself a fairly passionate programmer, I haven't found enough incentive to invest proper time to learn a purely functional language. The infatuation with Clojure and Haskell only lasted for a weekend for me. I always think, that next month I am going to invest in learning a functional language, but always something else more shiny comes along from other domain like, Dynamo DB, Firebase, RabbitMQ, etc. Which I find more practical to learn rather than learning yet another programming language.