Here's why:
* "Spanish" is an adjective describing the olives' origin. Adjectives are generally not capitalized unless they are part of a proper noun.
* "Olives" is a common noun, referring to a type of fruit. Common nouns are not capitalized unless they are at the beginning of a sentence or part of a proper noun.
Example:
* Correct: I bought a jar of Spanish olives at the market.
* Correct: Spanish Olives are a delicious snack. (Because "Spanish Olives" is used as a proper noun, possibly a brand name)
Exceptions:
If "Spanish Olives" is part of a proper noun, such as a brand name, then you would capitalize it. For example:
* Correct: I bought a jar of Spanish Olives from the gourmet food store. (If "Spanish Olives" is a specific brand)