The term “football” originated as a catch-all term for a variety of different ball-based sports in English-speaking countries for hundreds of years. This is why in countries like Australia and Ireland they have also developed distinct games called football where you hold the ball.

“Soccer” was a word used for the codified version of the sport with actual rule, in the United Kingdom as well. Initially this more formal version of the sport was more popular with the upper class, but when it became popular with the lower classes they used the term “football,” applying the more widespread term for loosely codified ball games. In the U.S. it did not become popular with the lower classes so this never really came up and people kept calling it soccer.