They're looking for self-validation. When you don't talk to them, you're not validating their existence. Some people will take it personally, and well, that's their own damn fault. Extroverts get their energy and validation externally, an introvert's energy and validation comes from within. That's why they bother people like you and me.
Yes, girls have asked me that question since as far back as I can remember. Recently, I just stopped giving a shyt. I realized that it's because they thought I was attractive because they didn't bother the other quiet asian ugly kid in class.
I was like "What about him? He's quiet too." she told me to stop trying to change the subject. lol