Why does AWS take a long time to change the password of DB Clusters?

I'm running this command to change the master user password of a DB Cluster on AWS:

aws rds modify-db-cluster --db-cluster-identifier development-db \
    --region us-east-2 --master-user-password newpassword --apply-immediately \
    --no-cli-pager > /dev/null

When I do this the status of the cluster changes from available to resetting-master-credentials. Sometimes it'll be in this status for minutes at a time and it just doesn't make any sense to me - I'd expect this change to be near instantaneous.

Any ideas as to why it wouldn't be?