Here's why:
* Action verbs describe actions, like "run", "jump", "eat", "write", etc.
* Adjectives describe nouns (people, places, things), like "tame", "big", "red", "happy", etc.
While you can use "tame" in a sentence that implies an action (e.g., "They tamed the wild horse."), the word "tame" itself doesn't describe the action. The action is actually implied by the verb "tamed".