Board Thread:Theories and Speculation/@comment-25093611-20160322113057/@comment-25122992-20160323222233

The main problem - Kakashi is not the true owner of these eyes (and only the original owners can truly handle these eyes' power) and he has neither Uzumaki's life force (as Nagato) nor Hashi's cells (as Obito, who still had issues with it anyway) to use it properly without exhausting himself immediately.