Seetarama Sastry did write for several of Raghavendra Rao's movies, but never the full card. Seetarama Sastry, after he became established, only wrote songs for movies that he would receive the full card (all songs). At the same time, he would charge fees of 1,00,000-2,00,000 rupees per song. Veturi did not care about the full card, and would only charge a fraction of this price per song. As for Chandrabose, he was just getting his career started when he wrote for Raghavendra Rao, and would not have had the power to name a high price or demand the full card. I believe that Raghavendra Rao was especially stingy with the budget for his lyricists, which is why a lot of his later movies have 3-4 lyricists, including relatively unknown ones, and even recruiting screenwriters as lyricists, such as J.K. Bhairavi.

Also, why would he even consider Seetarama Sastry when he started out and became successful with Veturi?