The reason Americans call association football "soccer" has historical roots related to the development of different sports in England and the United States.
In 19th-century England, there were different forms of football games. The two main types were Rugby football and Association football. To distinguish between them, people started using terms to differentiate. In 1863, the Football Association (FA) was established in England to standardize the rules of association football. At the same time, the Rugby Football Union was formed later for rugby football. To clearly separate the two sports, people in England began to use the terms "rugger" for Rugby football and "soccer" for Association football. The word "soccer" comes from "association" - the "assoc" part of the word, with the "-er" suffix added, similar to how other sports like "rugger" were named.
When these sports were introduced to the United States, both association football and rugby had some popularity initially. However, over time, rugby and its Americanized version, American football, became more popular in the US. As American football developed its own distinct identity and rules, the sport of association football needed a name to set it apart. The term "soccer" that was already in use in England to refer to association football was adopted in the US.
In other parts of the world, the term "football" is widely used for association football because it is the most popular form of the sport. But in the US, since American football is the dominant sport known as "football," the term "soccer" has remained in common use to refer to the sport played with a round ball and kicked by players (with some exceptions for the goalkeeper). So, the use of "soccer" in the US is a result of historical naming practices and the evolution of different sports in the country.
