On any wiki, it is natural for any contributor's activity to wax and wane. Sometimes, contributors go on hiatus but later manage to find the time to become involved again. Other times, for whatever reason, users are unable to come back to the site for an indefinite period of time, perhaps permanently.
For security reasons, IMSLP prefers not to leave users with over 6 months of complete inactivity with sysop rights—until or unless they return to activity, in which case they are restored on request of the user. Users that have been removed from adminship due to inactivity are placed into their own group, the members of which can be found.