So, its a bad authn practice that is maintained to mitigate the impacts of bad authz practices (you make authn less secure when people are intended to be authorized, in the hopes than when they aren't and you haven't cleaned up their permissions, the password expiration will cause authn failures so the fact that their authorization hasn't been revoked won't matter), instead of adopting good authn and authz practices?
If the former user had IT administrative and VPN access, it would otherwise take time to figure out who should still be there. It is faster to rotate the whole departments access to auto kick non-participants off the network. Then mop up the specific user logins, and migrate any orphaned user assets into the department share.
Keep in mind >90% of security breaches come from within firms. =3
It is mostly about ensuring some busy admin doesn't have to inventory every user permission.
Rotating domain logins form a similar function of booting inactive users.
2FA actually may make a system weaker, as people can MITM for $23 using a bogus telecom service and password reset. =3