Here's why:
* Adverbs modify verbs, adjectives, or other adverbs, providing information about how, when, where, or to what extent something happens.
* Ly-adverbs are a common type of adverb formed by adding "-ly" to an adjective.
Finally modifies a verb, indicating that something has happened after a long wait or delay.
Example: "After hours of waiting, the train finally arrived."
In this sentence, "finally" modifies the verb "arrived," telling us that the arrival happened after a considerable amount of time.