Why can't certain Civimail Mailings be reused?
The Re-Use link does not appear if either:


The user does not have at least one of the permissions (Create mailing OR access civimail) 


or:


If the mailing was created from Find Search >> Email - schedule/send via CiviMail (which creates hidden smart group) and have Unsubscribe Group field set.


Thanks

Pradeep