A common ploy when you're trying to make your name. They add theirs to your work and get a share of the royalties. Classic case is Buddy Holly's manager Norman Petty who added his name to the writing credits telling the gullible young writer that it would add credibility to the songs. I once had a song accepted by a group who had had three number one hits but they would only record it if I accepted their names as co-writers, thus giving them half my royalties. I refused.
signed,
Poor but honest!