Here's why:
* Adverbs modify verbs, adjectives, or other adverbs. They describe how, when, where, or to what extent an action is performed.
* Assiduously describes the manner in which something is done, emphasizing diligence and persistent effort.
For example:
* "She assiduously studied for the exam." (modifies the verb "studied")
* "He was assiduously dedicated to his work." (modifies the adjective "dedicated")