Elvis Presley - Milkcow Blues Boogie Lyrics

There are so many versions of "Milkcow" and usually the artist who does their own version of it is given writer's credit, or at least SOME. Kokomo Arnold wrote virtually none of this version, but some of the lyrics come from Wills' "Brain Cloudy Blues" western swing interpretation, but it is by no means identical. Not at all. Chord structure, tempo, and many other aspects are completely original here. But Elvis Presley is denied any credit AT ALL. And this was at Sun, where he had more freedom. I do not understand. Elvis was just at the right age to begin developing writing skills, and changed virtually every blues, and completely and totally revised "I'm Left, You're Right . . ." to a song called, by Phillips, "My Baby's Gone," but that one was sent to radio and quickly pulled. What was going on here? Why did even Phillips stifle Presley's artistic development? Why was he treated this way, even from the beginning. Does anybody have even a clue?
I mean, wearing a "kick me" sign on your back is one thing, but sometimes it's just ridiculous in the case of Elvis. Why did they not give him a chance? Only later did they attach his name to some Otis Blackwell tunes that he didn't write, and he stopped that by saying "makes me look smarter than I am." That is revolting when you consider his creativity and desire to branch out even at Sun. I just don't understand. Does anybody understand this? I mean, others got their "props."