It does work, it just doesn't compile to 64-bit.
GHC doesn't have an awful lot of people working on it, certainly compared to something like GCC. There is no maintainer for x86_64 on OS X; essentially, those of us without the skill to resolve the issues are just hoping that someone steps up.
This Trac ticket has more details; you can see from the length of the CC list how much interest there is in resolving this. Unfortunately, interest doesn't directly translate into a fix.