Why do people have their Facebook privacy settings where the public (or "non-friends") can see their stuff?

I can understand public officials, politicians, celebrities, people looking for publicity or not shy about their information having their privacy settings where everyone can see their stuff. I can’t understand why regular people have their privacy settings where the general public can see their photos, posts friends list, likes, etc.

Why do people have their FB privacy settings where non-friends can see their stuff?