It’s because of your capacity for empathy. They target you because they can appeal to your sympathetic nature, your ability to nurture; they often do so using manipulative tactics beyond your wildest imagination.
Narcissists flatter you in the beginning, often showering you in attention. They want special treatment, never 'what's on the menu' and they seek to control all those in their circle of relationships either overtly or covertly. They have a very fragile ego they are willing to do anything to hide therefore they seek to destroy those they cannot control.
You are sensitive because you treat others with reasonableness, honesty and integrity.
It’s mind blowing when others don’t respond with the same treatment. To a sensitive person, it’s completely devastating and it’s not something you can just shake off.