Here's why:
* Contractions are combinations of two words. They are created by merging two words and replacing some letters with an apostrophe.
* Example: "I am" becomes "I'm"
* Words, nouns, and pronouns are individual units of language. They have their own meanings and functions within a sentence.
* Example: "The dog barked at the cat." (Dog and cat are nouns.)
In short, contractions are a shorthand way of writing two words together, but they aren't words themselves.