Technical tools control and monitor all use of privileged accounts
Technical controls that log and alert on privileged session activity implement A.8.15's logging requirement for the accounts capable of the most damage.
Watching privileged sessions and alerting on unusual administrative activity is monitoring focused on the accounts capable of the most damage, central to A.8.16.
Vaulting admin credentials and alerting on unusual administrative activity constrains and watches the privileged sessions A.8.18 is concerned with keeping under control.
Vaulting admin credentials and alerting on unusual administrative activity gives A.8.2 the technical constraint and visibility it requires over privileged sessions.