More than a few years, the post was in late 2003 but the OS X preview came out in late 2000 where they clearly decided to not use X already. The decision was l

More than a few years, the post was in late 2003 but the OS X preview came out in late 2000 where they clearly decided to not use X already. The decision was likely made substantially before that date as well, not to mention NextStep.