“English usage

Whether usage of America or the Americas is preferred, American is a self-referential term for many people living in the Americas. However, much of the English-speaking world uses the word to refer solely to a citizen, resident, or national of the United States of America.

In addition, many Canadians resent being referred to as Americans because of mistaken assumptions that they are U.S. citizens or an inability—particularly of people overseas—to distinguish Canadian English and American English accents.^[67]”

That is why.