CDCK provides notifications for Meta and the sites they’re paid to host.
Fig provides notifications because the app itself is $20 a year, covering the cost of the notification service.
I’m sure this has been discussed and they will correct me if I’m wrong, but I don’t think it’s remotely practical to ask CDCK to pick up the tab for the notification infrastructure to route hundreds of millions of messages. After all, it’s a selling point of their hosting.