As far as I see (with my limited Haskell and Clojure knowledge), Haskell, being pure functional, has a much steeper learning curve than Clojure, which while mostly functional, focuses a bit more on being practical.

Furthermore, Clojure can use the already existing Java libraries, while in Haskell's case, the number of available libraries is considerably smaller. Clojure plays nicely with Java, so you can mix and match Clojure developers with Java devs, and they won't go for each other's throat.

Haskell doesn't play all that well with any other language.