Here's why:
* Action verbs show an action being performed. For example:
* Run: He ran a marathon.
* Think: She thought about her vacation.
* Linking verbs connect the subject of a sentence to a noun or adjective that describes or renames the subject. They don't show an action. Instead, they link the subject to information about it. For example:
* Be: She is a doctor. ("Doctor" describes her)
* Become: The caterpillar became a butterfly. ("Butterfly" renames the caterpillar)
Examples of linking verbs:
* Be: am, is, are, was, were, been, being
* Become: become, became, becoming
* Appear: appear, appeared, appearing
* Feel: feel, felt, feeling
* Look: look, looked, looking
* Remain: remain, remained, remaining
* Seem: seem, seemed, seeming
* Smell: smell, smelled, smelling
* Sound: sound, sounded, sounding
* Taste: taste, tasted, tasting
In short, linking verbs are like bridges that connect the subject to its description or renaming. They don't show any action happening.