Americans overseas have no formal voice at the legislative level. Their voice is diluted over the 50 states in which many of them vote. Some are not associated with a state so they only can vote in federal elections therefore they have no one to address any concerns.
The various American overseas organizations are fragmented hence no strong voice unlike other countries such as France (as an example). French expats have a delegate in each region of the world (e.g. Frédéric Lefebvre, the French expat delegate for North America) where he/she sits in the French National Assembly—therefore a formal legislative voice representing the interests of French expats. In other words, France values its expats unlike the United States which looks upon its expats with suspicion.
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Please note that it is not only Americans overseas who are in an untenable situation at present. The reach of the newly established Foreign Account Tax Compliance Act (FATCA) extends to green card holders living overseas, "accidental Americans" (i.e. those individuals who were born in the U.S. to non-American parents and left as infants, but are nevertheless considered U.S. Persons for the rest of their lives vis-à-vis taxation issues), non-American spouses of Americans overseas, and other countries' expats living in the United States where they have bank accounts, investment accounts, mortgages, et al. in their respective home countries. These individuals are having their accounts closed and mortgages rescinded as a result of FATCA.