The worst hack at a company I worked for was caused because an old server that was supposed to be decommissioned was left plugged in and connected to the network… a good time later, a hacker exploited a vulnerability in an unpatched package on the machine and got in (since the server was supposed to be decommissioned it was not patched when the rest of the machines were patched).
The hacker used old credentials on the machine to gain access to other machines in our network. If we had been rotating credentials more often, this would not have happened.
We had systems in place to patch and maintain our machines, but once the machine got lost in our inventory management system, it was forgotten about. It wasn’t monitored anymore, and other protections lapsed.
This category of exploit is prevented by credential rotation, because this type of exploit is only possible if a system is neglected.