But Lisp has been around for 50 years and never hit the mainstream so it seems there perhaps is something about it that doesn't fit with most programmers?
Also it only offers one form of concurrnecy and while I like it there is still much speculation and research in the area. Scala for example kind of builds on the whole Java-language and offers a more recognizable language for Java-developers and more opportunities to roll your own concurrency-mechanisms, or at least that's the impression I've gotten.
And then we have Haskell and Erlang.