Why are available updates of CKeditor not visible in the update report in Drupal 7?
Drupal only check for drupal modules. The CKEditor module is https://www.drupal.org/project/ckeditor and the latest version is 7.x-1.16. This information should appear in admin/reports/updates.

I suppose you are talking about the CKEditor library which is not handled by the page admin/reports/updates.