Daoist Baishi was the Archbishop of the Hall of Literary Glory, possessing a most esteemed status within the Orthodoxy. According to the rules written in the Daoist scriptures, even if an important figure of his level contravened the laws of the church, in order to bestow punishment upon him, the Pope would first have to open a meeting in the Great Hall of Light. Before the church, they would announce his crimes and then have the Hall of Drifting Clouds decide the punishment.
This was how the previous Pope had banished Mu Jiushi from the Li Palace.
The current Pope, Chen Changsheng, had not returned to the capital for three years now. Even if he returned to the capital to discuss Daoist Baishi's punishment, there might be people who would stand on Daoist Baishi's side, or at the very least request that he be spared the death penalty. Also, Shang Xingzhou was in the capital, and he would certainly not watch as Daoist Baishi was killed.