It was delayed due to middleware issues (things assumed to exist that didn't or were separate from the OSX licenses, and having to do more work than anticipated writing replacements), then delayed again due to the Enhanced Edition (by the time the engine was ported it was quite out of date, and updating it for both the original and Enhanced Edition wasn't feasible), and both the OSX and Linux versions of the EE were released after the console and Windows version (things just took longer than anticipated, and for a while it was uncertain if the Windows version would be ready for the already set console release [due to manufacturing requirements and the retail release]).
