I added a user to an organization. However, closed tickets for this user are not being added to the organization, why?
If you add a user to an organization, any tickets requested from that user that have a status less than Closed will be added to the organization too.
Closed tickets cannot be edited and therefore, they cannot be updated and associated with the organization. User and organization updates never apply to Closed tickets.
See What is the difference between Solved tickets and Closed tickets for more information.