Here's why:
* Subjects perform the action: The subject of a sentence is the person, place, or thing that is doing the action described by the verb.
* Verbs describe the action: Verbs are words that describe the action or state of being.
Example:
* The dog barks.
* "Dog" is the subject (performing the action)
* "Barks" is the verb (describing the action)
Think of it this way: A verb needs a subject to act upon. It can't exist independently as the subject itself.