Reason for root `/private` heirarchy What is the reason for the /private directory structure located at the root of an OSX system volume?  Why are /etc, /tmp, and /var symlinks to subdirectories of /private?

NOTE While writing my question, I discovered this answer to another question which seems to address this issue.  I'm going to post my question anyway because it contains the terms that I searched for.  The other question/answer doesn't, prompting me to start writing this question in the first place.
This answer to another, more specific question explains that this directory structure quirk is a vestige of OSX's NextStep heritage.