Render Drupal variable in CKeditor
First thing is this its not a good practice to write the php code in CKeditor because it impact the execution of page and increase the page load time.
So it would be better to create the specific page tpl and and render all the drupal variable there.

Reason ::  Why its not rendering the drupal in CKeditor because after the complete page load its execute the content section of CKeditor and at that page has not page drupal variable (now page has only html content).

Thanks