Here's why:
* Common nouns refer to general, non-specific people, places, or things.
* "Street" is a general term that can refer to any street, unlike a proper noun like "Main Street" which refers to a specific location.
Think of it this way:
* Common noun: street, car, dog, house, book
* Proper noun: Fifth Avenue, Ford Mustang, Fido, White House, Harry Potter
Let me know if you have any other questions!