Because it's called football, if American football was the original one it wouldn't have American in front of it and "soccer" as you call it would be called European football (not sure about the original country but I think the first variation started in Greece).
They call it soccer to try and avoid confusion between football and American football.
The correct name of the sport is Association Football. The term "soccer" is just a slang term derived from the word association.
FIFA is the world governing body of the sport. Federation International FOOTBALL Association.
If you do some studies. soccer is a style of playing football.
Because the main idea of the game is to control the ball with your feet only.
Because other countries don't call it soccer.
soccer is called by USA
football is called by UK
Mainly because you hit a ball with your feet.
***** please.. Its football which is also known as Soccer.