For a suspended account there is option to list reason for suspension that is both sent in e-mail and displayed on user card:
I agree that automated message is a little odd to be sent when an account is silenced as a staff action, because it reads that account is only on hold until a staff review.
Edit: Could be set as that because silencing can be an automated action as well as manually done by mod/admin. Then user account that has been silenced can still talk in PM topics but just can’t start new ones or public topics.
With suspension PMs wouldn’t make sense because user can’t even login to read those, so e-mail would be the only way to communicate.