Why can't a billing manager see the linked account?

So it was quite a trick just to get a secondary email account activated for the purposes of being the all-accounts billing manager but we go that figured out and activated.   Didn't occur to me you had to login as the actual secondary user to activate the account, so I guess stupid on my part. 

HOWEVER things still don't work as desired.  I can login with the billing manager user now and the user sees the PRIMARY account but none of the linked accounts.  Eventually we're going to have 5 or 6 (and possibly more, some day) Comcast Business accounts linked to the primary but the secondary billing manager has no apparent visibility in to the bills of each linked account, which is a huge problem.  I want the billing manager to get all the bill notifications, not us in IT.  If service gets disconnected at any of these sites for lack of payment it's bad news for us.

If the account is linked to the primary and the user has billing manager access to the primary account why can't they have billing manager access to the linked account - or, at least, have the option of adding their account to have access?  If I go to the linked account "Users" the Billing Manager I created in the primary account is not listed there.  If I try to manually add the user, the system complains that the user is already registered.  GREAT.  

I think I may just have to switch over our accounts payable as the primary manager just so they can manage and pay things correctly but brother it's infuriating not being to manage their access instead.  Our company's IT would kind of like to continue to manage certain things ourselves but man this is just really silly the way it's done.