Feng Jun had not previously announced that Bai Mu's true identity was a person from Ni Hong, because he intended to catch Kunlun off guard.
If Kunlun were informed and prepared, they might have corresponding measures to take—just as Wangwu showed up uninvited.
In general, his accusations against Kunlun were successful.
First, Kunlun's aggressive acquisition had always been criticized. No one had acted out before, partly because Kunlun's power was too great and they were quite secretive, meaning that even if others were unwilling, they were helpless.
Now that a transcendent being had initiated the challenge, there was no problem for the Daoist Sects to rally and support the cause.