Performers such as Williams find it impossible to handle copyright on their own, hence association with Acuff Rose, which was affiliated with BMI.
I should have said Williams was the composer; he assigned the copyright so that Acuff Rose could handle royalties and business matters connected with it and other of his compositions.

The company was taken over by Gaylord-Grand Old Opry, and in turn that was purchased by Sony-ATV, recognized by BMI and now the largest publisher of country music.