Can't add friends from your Nintendo Friend's List

It's pretty weird to me that you can't add friends to Miitomo that you have on your Nintendo account. You're stuck with only being able to add people via Facebook, Twitter, and face to face. I can understand why Nintendo is hesitant to allow anyone to add anyone else, but I would have thought they would have at let you link your Nintendo friends to your Miitomo. I don't have a Facebook or Twitter, but I have friends on my Nintendo friend list I'd like to talk with on Miitomo.