Why might black musicians have been commercially less successful than white musicians in the 1950s?
As a result of racial discrimination.
The music industry was segregated, particularly with respect to broadcasting. There were white stations and black stations. Great blues artists such as Muddy Waters and Howlin' Wolf made very little money for most of their careers.
Their access to millions of white listeners and thus the white market was almost non-existent.
When Chuck Berry first had success he found that his songs were credited as being co-written by broadcasters such as Alan Freed as an example of payola, that is having to pay someone to get their music played.
A number of factors however led to greater commercial reward for black musicians. Firstly Elvis Presley's first single was That's Alright Mama which was a Big Bill Broonzy song. That introduced a white audience to black music. In fact, initially, many listeners thought that Presley was a black singer.
Secondly the establishment of the Chess Label in Chicago promoted musicians such as Berry and Waters.
Finally the commercial success of British bands covering blues numbers again brought recognition of black music to the white American public.
This was particularly true of The Rolling Stones who covered songs by Chuck Berry, Muddy Waters and Willie Dixon, amongst others.
Keith Richards tells the story of when they went to Chess studios to record, Muddy Waters was painting the ceiling.