Here's why:
* Nouns are words that name people, places, things, or ideas. Examples: *dog*, *city*, *table*, *freedom*.
* Pronouns are words that replace nouns. Examples: *he*, *she*, *it*, *they*.
* Adverbs modify verbs, adjectives, or other adverbs. They tell us how, when, where, or to what extent something happens. Examples: *quickly*, *yesterday*, *here*, *very*.
So, nouns, pronouns, and adverbs are all different parts of speech with distinct roles in a sentence.