In 19 century, people were racist, why Josh White was still very famous? Had so much white audience?

"People were racist" doesn't mean anything. It is a current fad expression calling up preprogrammed patterns of hate. Racist people don't consider themselves racist, they are merely obeying the laws of the universe. For example, you don't call yourself a pejorative name just because you don't let your dogs sit on the furniture, you just don't want your furniture torn up. Likewise, people of the 20th (not the 19th) century had attitudes that modern people can't even imagine. If you study the history you will find that he was severely mistreated in the 40s, in spite of his talents.