Authentication caching and password changes

In Dovecot docs (https://doc.dovecot.org/2.3/configuration_manual/ authentication/caching/) we see:

1. User logs in with password Y. The cached password X doesn’t match Y and the previous authentication was unsuccessful, so Dovecot doesn’t bother doing another backend passdb lookup (until cache TTL expires). The login fails.

Anyone knows why they chose this design ? Why not simply do a passdb lookup instead of waiting for cache TTL to expire ?

In Dovecot docs (https://doc.dovecot.org/2.3/configuration_manual/ authentication/caching/) we see:

1. User logs in with password Y. The cached password X doesn’t match Y and the previous authentication was unsuccessful, so Dovecot doesn’t bother doing another backend passdb lookup (until cache TTL expires). The login fails. Anyone knows why they chose this design ? Why not simply do a passdb lookup instead of waiting for cache TTL to expire ?