Because it is the correct way to spell in the English language.
Here in the US of A we have butchered every language and smashed it together to make it our own. We usurp words from other languages and pass them off as ours (kindergarten for example.....it is German).
Oh and then we have the lovely "rules" of spelling. Like:
I before E except after C and when it sounds like A as in neighbor and weigh....then there is the word "weird" which does not fit the rule.
And people wonder why immigrants have such a hard time learning the language....WE barely understand it!!!