Here's why:
* Adverbs modify verbs, adjectives, or other adverbs. They tell us how, when, where, or to what extent something happens.
* "Abruptly" describes the manner in which something happens.
For example:
* The meeting ended abruptly. (modifies the verb "ended")
* He was abruptly dismissed. (modifies the verb "dismissed")
* The music stopped abruptly. (modifies the verb "stopped")