What is Single Logout and why is there such limited support for it?

Single Logout (SLO) is a feature that allows users to sign out of every application they are logged into with a single action. It ensures all active sessions are closed at once and prevents potential vulnerabilities from remaining open. However, despite its benefits, SLO has limited support due to technical complexities, lack of standardization across SPs, user experience issues, and varying implementation among IdPs. Despite these challenges, SLO can still help reduce the number of orphaned sessions and improve overall security.