@igotnopicks
Because they’re all distantly related. You can even see the vague similarities: large teams playing on a vast and mostly unmarked field, goals at the very end of the playing area (unlike, say, hockey or lacrosse), no equipment except for protection, and no weather delays unless there’s a friggin’ meteor.
In the old days, “football” wasn’t a sport so much as a mosh pit with goal lines. As time went by, different places came up with different rules to keep the casualties to a minimum. One of the first things to go, evidently, was advancing the ball by throwing it, which is why it was such a big deal when American football introduced the forward pass. (And if you look at all the rules in place now to protect the poor bastard trying to catch a pass or a punt, you can understand why it was banned.) Beyond that, some places put more of an emphasis on kicking the ball, laying the groundwork for modern soccer, while others encouraged running the ball, which would evolve into rugby and its offshoots.
Of course, soccer would go on to become wildly popular, because kids could play it without breaking their tiny skulls, and in a lot of places it was the only “football” they’d ever know, hence the modern naming controversy.