I think it's because Clojure itself has been offering a better alternative to streams for years. And let's be honest: @FunctionalInterfaces are a compiler hack

I think it's because Clojure itself has been offering a better alternative to streams for years. And let's be honest: @FunctionalInterfaces are a compiler hack, since Java doesn't really have functions. And what I simply love about Clojure: If writing (reify java.util.Function (apply [this arg])) is too verbose, roll your own macro or function. You could also add a tagged literal.