why isn't american football called american rugby?

Because it's the variety of "football" most common in America. Just the way that the word "football" refers to Rugby Union in New Zealand or Wales, Rugby League in parts of Australia but Australian Rules in other parts, or to Association Football in most of Europe.

You've got to remember that there is a wide variety -- probably dozens --of "footballs" played around the world. What they have in common is an origin in village and school games which were played on foot (as in "foot" soldier) and with a ball. Hence, the generic name "football". It has absolutely nothing to do with the way the ball is played.

Because in the ancient Americas, they played a game very similar to modern American Football where the ball was the severed feet of the previous games' losers. That's why it's called football.

It's been called football for about 150 years. It's time for you soccer people to move on.

Well TBH to you Football (Soccer) and Rugby(Football) have a common origin, In North America people call rugby as football because the size of the ball is that of foot whereas rest of the world call soccer as football because it is played with foot

Well in short it is that Americans adapted the name of Rugby as football when rugby and football(soccer) got separated

Basically in rest of the world soccer is called as football because of major world events like FIFA UEFA La liga etc

Whereas as in USA events like NFL made the name football(rugby) famous..

Because man who created american football decide call American football

American rugby? That just sounds g@y.

We call it football to piss people off.

Because it annoys the foreigners, and we Americans like to do that.

Even if the word "soccer" is a British invention...

A rectangle is more like a square than a circle. Should we start calling all rectangles squares even when there are differences between them?

Because it was named football you twerp. Besides, it is played with only one foot so it makes sense. Also, there is no rug on the field so that cannot be.