It makes for a cleaner OOP-y interface in which the caller only cares about actually exposed properties and not methods to get and manipulate hidden properties.

IMHO using properties directly is a much more natural way to talk about objects, than having a bunch of methods to get properties. Getters and setters also help ensure that methods are only for changing an object's state, not getting an object's state. For example:

  class User{
      public ForumsPost $LastForumsPost{
          get{
              if(!isset($this->LastForumsPost)){
                  $this->LastForumsPost = <get from database...>;
              }

              // Return the cached property so we don't keep hitting the database.
              return $this->LastForumsPost;
          }
      }
  }

  print($user->LastForumsPost->Title);
  print($user->LastForumsPost->PostId);

  // instead of...

  print(($user->GetLastForumsPost())->Title);
  print(($user->GetLastForumsPost())->PostId);