Why wouldn't you host your add-on via RTB?
That mediafire direct link is temporary, so you can only use it if you like updating your topic with a new link every couple of hours.
It doesn't do session or referrer verification?
If it did it still wouldn't work, but when you request the mediafire download page it transfers the file to a download server temporarily. The file is later removed from that server, so the direct link is no longer valid.
Want to provide a mirrorAre worried it will be lost / archived (didn't that happen with RTB2 to 3 or something)Banned from the service
I mean, in addition of that, you'd expect them to do some kind of anti-hotlinking.
The first two reasons seem to be one and the same.
I don't have much sympathy for them though as they must have done something quite bad to warrant it.