Here's why:
* Contractions are primarily verbs. They are shortened forms of two words, typically a verb and an auxiliary verb (e.g., "I am" becomes "I'm").
* Adjectives modify nouns. They describe or give more information about a noun.
* Contractions don't inherently modify nouns. For example, "She's happy" doesn't describe a noun, but rather the state of the subject "She."
Possible exceptions:
* Informal language: In very informal speech or writing, contractions might be used in a way that *sounds* like an adjective, but it's not grammatically correct. For example, someone might say "That's a great 'cause" to mean "That's a great cause." This is more about casual usage and wouldn't be considered proper grammar.
* Unusual constructions: There are some extremely rare cases where a contraction might be used in a way that functions as an adjective. For example, "That's-a-way" could be seen as a slang adjective meaning "that direction." However, these are highly unconventional uses.
In general:
It's very uncommon to use contractions as adjectives. If you're looking to modify a noun, it's best to use a proper adjective.