One historical explanation is that it was due to the popularization of sales culture in the 20th century which began around the 1920s, and greatly accelerated after WWII.
Another historical explanation, as has been mentioned by other commenters, is that it was due to the popularization of African American culture.
But of course, they are just two of the many plausible historical explanations.
Another historical explanation, as has been mentioned by other commenters, is that it was due to the popularization of African American culture.
But of course, they are just two of the many plausible historical explanations.