If a profile is entered with a birth date and a death date is not entered nor is "about/uncertain but non-living" checked, the profile will be automatically unlisted. If the person is living, the profile will be unlisted. (I believe this is if the birth date is under 100 years before current date.)
Unlisted cannot be assigned if the person has passed away. Anyone creating a profile can assign this privacy protection.
More info: https://www.wikitree.com/wiki/Help:Extra_Privacy