It makes sense if the US government is not giving you any benefits while your living outside of it's country besides a Passport, why pay taxes for services you are not going to use.
As long as the passport is good may as well just become a citizen of the country you emigrate too any pay their taxes not get double dipped on.
It is based on the rights to use. If you are American citizen, you rights to use the service any time later. You are also protected by the American Military all over the world.