Here's why:
* Subject: It's missing a subject, which is the person or thing performing the action. We don't know who "you" refers to.
* Verb: "Love" is a verb, but it needs a subject to act upon it.
To make it a complete sentence, you could add a subject:
* "Do you love strawberries?" (This is now a question with a subject "you".)
* "I love strawberries." (This adds the subject "I".)
* "She loves strawberries." (This adds the subject "she".)