Using classic Outlook for Windows in business environments
It doesn't work because rules do not apply to emails that are being delivered to the Junk Email folder. Rules only apply to emails that are being delivered to your Inbox folder.
Therefore, you'll need to run the rule manually so you can pick the folder to run it against or via a macro so you can achieve it with a single click.
Another alternative would be to simply not care (too much) about the emails in the Junk Email folder ;-)