I've now subscribed to all of them manually, but it would be much easier with the one-click button.

When editing your playlist in "edit basic collection information" you'll see an option where it says "What kind of collection is this?" you'll see two options you can check. "Items that work together" and "Items that users should choose between". If you checked the latter option then it removes the Subscribe to All and Unsubscribe from All buttons, but if you check the first one then they'll show up.