Contacts behave slightly differently between transactional and marketing emails (campaigns and loops).
Your Audience only contains marketing contacts. If a new contact is sent a transactional email, they are not added to your Audience.
Thus, sending a transactional email to a new contact will not trigger the “Contact added” loop trigger.
The “Subscribed” contact property does not affect transactional emails. Unsubscribed contacts will still receive all transactional emails they are sent.