Here's why:
* Adverbs modify verbs, adjectives, or other adverbs. They tell us how, when, where, or to what extent something happens.
* In a sentence, "elaborately" would answer questions like "how?" or "to what extent?"
For example:
* The artist elaborately designed the mural. ("Elaborately" tells us how the artist designed the mural)
* The cake was elaborately decorated. ("Elaborately" tells us to what extent the cake was decorated)