One of my kids gave me Atlantic Rhythm & Blues 1947-1974 for Christmas. (I have good kids.) 
I’ve never heard of some of the artists in the early volumes, but damned if I don’t know the words to the songs, from the cover versions that were played on the radio in the rural midwest, where I grew up, in the 50’s.
Two questions:
Why covers? Was it marketing, to cover all the bases, and to allow for racism – stations thinking white audiences wouldn’t listen to or buy black music?
Were the covers played in other parts of the country too, or did people living in urban areas and the South hear the originals? Did you have a choice? (I don’t remember ever tuning in anything that sounded like an R&B station in the 50’s, and my radio sometimes brought me Texas and Canada stations.)
We got Bobby Vee (Devil or Angel) and Ray Peterson (Corinna Corinna). Did the rest of the country get The Clovers and Joe Turner?
I don’t remember hearing black artists on the radio or seeing black artists on TV until the late 50’s, early 60’s, but I was hearing these songs, done by other people. I wanna know why.
“White” mainstream radio wouldn’t play “Black” music in the 50’s. But the songs were good, so they were covered by white artists. Seehere for more details.
Remember – in the 50s, most mainstream performers did nothing but covers. It was rare to have anyone write their own songs; they would just pick songs they liked from other songwriters. Songwriting and singing popular songs were two different disciplines, and the idea was that the composers usually didn’t have the voices to sing a hit song, and the singers didn’t have the talent (many couldn’t play instruments) to write anything of note.
It began changing in the 50s with the arrival of rock, but it wasn’t until Bob Dylan and the Beatles that the singer-songwriter was considered the way to go.
So 50s singers – even rock 'n roll greats like Elvis – did other people’s songs.
As for the race issue, Black R&B musicians were considered “race music” and their songs were only played on radio stations catering to a Black audience. These were generally in the South and in northern Urban areas, and few whites listened. However, many of those who did were out creating rock 'n roll – a version of the rhythm and blues these stations played (with a smattering of Country and Western).
White musicians would pick up on some of these and do covers (not just them – Chubby Checker, for instance, became a star covering “The Twist”). The covers were generally more popular – they were on bigger record labels, which could afford to get them into more stations (and pay more payola).
The general pattern was that the Black R&B group would release the song to become a minor hit (maybe in a single city – each station had its own playlist, so there was a lot of variation). A white artist would get word of it and rerecord it. Usually, Blacks bought the original, while Blacks (those unfamiliar with the original) and Whites would buy the cover.
While racism played a part, the fact was the white artists songs were more popular, and usually overshadowed the original (the same thing happened with “Blue Suede Shoes” – it was associated with Elvis and you rarely saw Carl Perkins performing it, either). People in the 50s were willing to accept Blacks in the role of entertainers, as long as they didn’t ask for equality. 
Well, to be fair, there was quite a lot of collaboration between black and white musicians. Steve Cropper and “Duck” Dunn are white, but worked with Eddie Floyd, Otis Reading and a bunch of others. I don’t remember if they were on Atlantic or Stax, though.
Atlantic also released Led Zep, so I don’t think it can be said to be a “black” label, the way Motown tried to be.
(my emphasis)
This is why the songs were covered in the first place, covers keep occuring today for the same reasons. Others here have explained well why the originals were wrongly “neglected.”
Thank you all very much. I hadn’t considered the evolution from covers to originals. I never paid much attention to who wrote the songs I was hearing.
I would have liked to hear this music when I was growing up, but I’m glad to be hearing it now.