Though it may come across as American ignorance, Britain is to be blamed for football being called soccer.
At the beginning of the 19th century, some universities in Britain made different variants of the medieval game football. Each version of the game was given a unique name. In 1863, the Football Association was formed to promote the game. They wrote the rules of the game we know as football today.
But during that period another version of the game was popular too. It was called Rugby football, named after the boarding school Rugby. Yes! The game of Rugby football owes its name to the school.
In this variant, the players carried the ball in their hands and ran towards the goal. The name was shortened and called 'rugger'.
The version that was played following the rules of the association was known as association football. But later on the word 'Association' was shortened to 'asoccer', which later changed to 'socker' or soccer'. But why was the word being shortened? It was a common trend to shorten words and add -er to it in Britain, such as soccer and rugger.
Meanwhile, USA took both rugby and, football and combined them in to one game. It was coined Gridiron football. But the public never bothered with the first word and called it plain 'football', despite the fact that it is mostly played by hand and the 'ball' is more like an egg than a sphere.
As a result, American football players started calling original football by the name of soccer, to avoid confusion. The governing organisation of the game also changed its name to United States Soccer Association.
The interesting thing is, from 1960 to 1980, both 'football' and 'soccer' were used to define the game in Britain. But while the word 'soccer' gained popularity in the US, its usage declined in Britain.
So this is how, Americans ended up calling the game soccer while the rest of the world called it football.