I get it now. They simply failed to block out the menu option for adding ringers to groups.
While I see that the group thing is used mostly for distribution lists, it's handy for other stuff as well. I put every carry-out place my wife and I like in a group, then I can find them quickly when hungry.
Oh, and they already give you the option to add home and office phone numbers to groups, not just email addresses and cell numbers. So they really wouldn't have to go far to make this happen.
For years phones have been doing the whole caller group with ringer thing. It seems short-sighted to not use this existing infrastructure for this purpose.