Why do white people and Biracial people want every lightskinned Black person to be Biracial?

Im like the rapper T.Is color and people some times ask if im mixed... and i look at them like there stupid.. All black people dont have to be super dark to be black... Look at Malcome X, he was really light skinned. He was more pro black then anyone.. What about Huey P Newton who started the Black Panthers.he was as light as Alicia Keys . No one questioned them and said you cant be black, but when i post questions about beautiful Black women like Rihanna Beyonce and Christina Millian saying that they look bette then any white women people will say there mixed...But i did the research and Millians dad was half Cuban and Half African and her mom is 100% black, Rihanna is from Barbados which is a black country her dad is light but looks like Sammy Davis JR and her mom is Dark and kind of looks like Aretha Franklin so how is she Mixed, and Beyonce is 100% Black i saw her sister on Oprah Talking about how proud they are to be black during the Chris Rock good hair special. So why do people try to say that their not Black why do people try to say im not black is it so unbelievable that Black people can be attractive to you... White People tell me this??????