What's your alternative? Other countries have similar one-word names for their citizens, "Italians," "Japanese," "Mexicans", etc. United-Statesians? Then we might get the complaint that many other countries are made of smaller states too! Let's go for "citizens of the United States of America," that's nice and short. I get that Central/South America exists, but let us have the word, there's nothing else which sounds good.
What's your alternative? Other countries have similar one-word names for their citizens, "Italians," "Japanese," "Mexicans", etc. United-Statesians? Then we might get the complaint that many other countries are made of smaller states too! Let's go for "citizens of the United States of America," that's nice and short. I get that Central/South America exists, but let us have the word, there's nothing else which sounds good.