For white people who had gone to traditional churches and heard a pipe organ, to hear an electric organ sounded bizarre. They thought blacks were playing a novelty instrument. Black people made innovations on the saxophone and white people thought the saxophone was a novelty instrument. And they did the same thing with the Hammond organ. Blacks were drawn to these instruments to find their musical expression.
Rap is a type of music that has evolved in much the same way.
You say 'Everyone is copying rap. But there's a certain kind of expression within rap music that cannot be copied by white people. Absolutely cannot be copied by white people, no matter how much they may be able to copy the form. It's like writing a sonata. That doesn't mean that what you did is Mozart.