Here's why:
* Pronoun: It stands in for a noun (e.g., "They" could represent "The students").
* Subject Pronoun: It acts as the subject of a verb (e.g., "They went to the store").
Verbs are words that describe actions or states of being (e.g., "go", "are", "think"). "They" is not describing an action or state of being, so it's not a verb.