Dunno. I'm Canadian. We consider the United States the "Americans" because a) they are called the "United States of America" (key point, "America") and b) America can easily be considered the poster boy/girl for North America due to their culture and influence on the world abroad. Canada and Mexico find it hard to compete with that, and while I can't speak for Mexico, I find the people of the United States more than a little backward. But, they probably see Canada the same way, so we're even.
People probably get upset because they dislike the idea that the U.S.A. has taken on the main role of representing North America, and in the wake of the financial crisis, war on terrorism, etc., I know a lot of Canadians (and a few Europeans) who find that the U.S. has made some, well, questionable decisions. As for people in the U.S., they probably don't like the name because they have heard how the rest of the world considers their stereotype (look it up, I`m not stating it) and do not wish to be lumped into the same group.
That`s just my guess, anyway.
People probably get upset because they dislike the idea that the U.S.A. has taken on the main role of representing North America, and in the wake of the financial crisis, war on terrorism, etc., I know a lot of Canadians (and a few Europeans) who find that the U.S. has made some, well, questionable decisions. As for people in the U.S., they probably don't like the name because they have heard how the rest of the world considers their stereotype (look it up, I`m not stating it) and do not wish to be lumped into the same group.
That`s just my guess, anyway.