It seems that for almost any popular piece of C or C++ software there are people who are motivated to produce a pure Java implementation. For whatever reason, you don't see that motivation in other language communities. Outside of Java-land, most feature-for-feature copies of existing software seem to be undertaken for the sake of learning or linguistic patriotism, which are not sufficient drivers to sustain such a project to completion.
My guess is that this phenomenon reflects the fact that other language communities have greater comfort and facility with C libraries, or to look at it another way, the fact that complete independence from native libraries is actually a feasible goal for most Java projects.
No one uses Haskell, or no one uses those optimisations?
Haskell has plenty of industrial users and quite a few very large programs as well. Those libraries hardly look mature - I know that many of the container libraries on Haskell make extensive use of unpacking, for instance.
