Here's why:
* Modal auxiliary verbs are helping verbs that express possibility, necessity, ability, permission, or obligation. They are used in conjunction with another verb (the main verb) to form a verb phrase.
* Pronouns are words that replace nouns, like "he," "she," "it," "they," etc.
* Nouns are words that name people, places, things, or ideas.
Examples of "would" as a modal auxiliary verb:
* I would like some coffee.
* Would you like to go to the movies?
* He would have helped if he had known.