Here's why:
* Modal auxiliary verbs help express things like possibility, necessity, permission, and obligation. They always come before another verb (the main verb) and help to modify its meaning.
* Verbs are words that describe actions, states of being, or occurrences.
Examples:
* May I borrow your pen? ("May" is a modal auxiliary, "borrow" is the verb)
* It may rain tomorrow. ("May" is a modal auxiliary, "rain" is the verb)
In summary: While "may" is used in a sentence to express possibility, it doesn't act as the main verb itself. It works in conjunction with another verb to create a complete sentence.