In the past OSX has actually been a pretty decent server OS. I wouldn't recommend it for that today, but there are still plenty of reasons someone might want it

In the past OSX has actually been a pretty decent server OS. I wouldn't recommend it for that today, but there are still plenty of reasons someone might want it (legacy systems, developer familiarity with OSX from desktop use, some Apple technologies that are useful even outside a GUI, and so on).