Why we're called Americans ... because of Europeans ...
Just to stop any war starting here my point is that Americans would hate being called Canadian and vice versa.
Just FYI, every now and then some people think it is we Americans (US citizens) who arrogantly called ourselves Americans.
It was Europeans who decided to refer to us as Americans, and did not differentiate from the fact that the United States were only a small portion of the two Continents.
The US from day 1 called itself the "United States of America," referred to ourselves as "the first American nation," etc... recognizing we were smaller than the whole.
There is a lineage of the word "statesman" among others that were quickly dropped in favor of being "blanket categorized" as "Americans" by various leaders of European nations on down.
In modern Spanish and several other languages, we are referred to as North Americans (e.g., Norte Americana).
Even I take great pains to avoid using the general term, as well as clarifying when I use the term "football," among other ambiguous/assuming terms.
Americans are considered "dumb" by many foreign citizens, but it may begin with their own history more than ours.
And then our US TV media only adds to it, as the most unintelligent American is the one watching 8+ hours a day (often jobless for years, or the non-working person in the family who still spends their income), still drives its advertising dollars and the resulting content of the TV.