There was no need to talk about how An Xuecheng proclaimed that he wanted to kill Mo Wuji just as he arrived. Even if An Xuecheng hadn't said it, with what the West River Religious Order had done to the Human Race in Cosmos Edge, it was undoubted that Mo Wuji would kill him.
At the same time, Mo Wuji knew that his abilities still weren't enough. Just because of 10 over Immortal Emperors, he had to use his Book of Luo. If he was going to engage in a war with the entire Gods Race, he would need to gather more power. Thus, if he eliminated An Xuecheng and Mifei Trade Union, he could gain a large territory within Cosmos Edge.
Seeing that Mo Wuji had completely no intentions of stopping, An Xuecheng promptly decided to escape towards his West River Religious Order; there was a transfer array there.