Here's why:
* Conjunctions connect words, phrases, or clauses. They don't dictate the grammatical function of the following word.
* Nouns can have various roles in a sentence: Subject, object, object of a preposition, appositive, etc.
Example:
* "I went to the store and bought apples."
* "Apples" is the object of the verb "bought."
* "The cat and the dog are friends."
* "Cat" and "dog" are the subjects of the verb "are."
Key point: The noun following a conjunction will be whatever grammatical role it plays in the sentence.