People identity is not just the country you are born and living. Their mentality , their culture, way of thinking and many more things are aligned with Nepal and Nepali culture who can not disassociate with it.
Ignorant and arrogant people are found every were and your question is one of them. Look at the 5-6 million Indian people who become Nepali citizens do not not consider it their county still may be loyal to India?
Unfortunate these people were victims of Nepali immigration rules who could not follow as Indians and become a landless people. By nature and by emotionally they were not Bhutanese what should they call themselves ?
Why on earth you tell people you are Nepalese even after taking US citizenship? If you able to answer it you will find your answer.
So you are thinking that you are superior than these people and looking them down? You are another AH person.