After the Emperor forced an irresistible deal upon Sheng Tian, the Third Pillar tried one more time to dissuade his majesty to not allow Sheng Tian to have a say in the matter of his successor, but failed in doing so.
Sheng Tian naturally wasn't going to give up this opportunity now that he knew even Wu Di doesn't know the whole truth, while the Emperor had his own plans that were unknown to anyone.
Long Chen, Tang Fei Yun, and Shang Shi Huo all sent Sheng Tian voice transmissions. Mostly detailing why Sheng Tian should go back on his word and not do as the Emperor says. The choosing of the succeeding Emperor is a huge ordeal, concerning the fates of millions of lives.
Naturally, they did not want such a large burden to fall onto Sheng Tian's shoulders, whom they are connected with. If something goes wrong, they will have some problems plaguing them and their powers.