A question about why this happens?

Ever since I was young, people have asked me if I'm mixed. One time this girl was like "oh my god, you're so pretty! are you mixed?" I told her no, but she still kept on insisting that I looked mixed. Now when I got into high school, this White guy was like "Wow, you look like Maya (the singer), are you half Italian (Maya is half Italian and half Black, that's why he asked). Then when I worked at the mall, my coworker asked me if I was mixed, and I told her no, and she said that I could pass for "one of those pretty biracial girls (her words, not mine)". I even had a biracial girl ask me if I was biracial. Some other Black girls have been talking crap about me, they said that I think I'm better because I'm mixed, and wtf I'm not even mixed, both of my parents are Black. I don't get why people ask me if I'm mixed...