Here's why:
* It's a common noun: "French dressing" refers to a type of salad dressing, not a specific brand or person.
* It's not a proper noun: Proper nouns are names of specific people, places, or things (like "France" or "Caesar Salad").
Examples:
* Correct: I like to put French dressing on my salads.
* Correct: She bought a bottle of French Dressing at the store. (This is a brand name)
* Correct: French dressing is a popular choice for salads.
* Correct: The chef whipped up a delicious French dressing.