United States Bhutan Relations?

I have found plenty of information that the United States & Bhutan don't have any relations accept informal relations through other nation's embies. Yet I can't find any information on why we don't have relations with them. They aren't a communist nation they don't support terrorism. Yes they use to be a monarchy but we have relations with other monarchies also they just had national elections so they have become a constitutional monarchy. So I don't understand why we have no formal relations with a nation that seems like its not hurting anyone, so if you can find any reason why we don't have relations with Bhutan please explain it to me.