Here's why:
* Pronoun Case: "Us" is the objective case of the pronoun "we". It's used when the pronoun is the object of a verb or preposition. "Juniors" is a noun, and needs a verb or preposition to connect it to the sentence.
* Incomplete Thought: "Us juniors" doesn't express a complete thought. It's like saying "The cat" - it doesn't tell us what the cat is doing or what happened to it.
Here are some examples of how to use "us juniors" correctly:
* As the object of a verb: "The teacher gave us juniors extra credit."
* As the object of a preposition: "The new policy affects us juniors directly."
To use "us juniors" correctly, you need to place it within a sentence that provides context and grammatical structure.