Answer: because American English is actually comprised of many other languages. So you are not learning just one language. Plus, English (as a whole) is content dependent for it's meaning . Look at the word "scale" in an English dictionary. It has 17 different meanings depending on how it is used. Talk about confusing the folks trying to comprehend this language!

Didn't you know that beauty is in the eye of the beholder. That's why eyedrops and rose-colored glasses are needed.