you dont have an xbl/psn account linked to it, or have facebook linked.
Seriously, bungie, you could literally be making some ancient members disappear due to this.
How fucking shitty is that?
Linky to info
https://www.bungie.net/en/User/Sunset?id=Wlid&sourcekey=orphan
-
You can sign up to XBL with your alternate emails, and get a Silver membership. Makes it a little more difficult to make alts, but easily dodged.