Zhou Tian, when not in a position of advantage, watched as those powers one by one hesitated to exert themselves, fearing that their own strength would be damaged in the struggle against him. However, once Zhou Tian truly exerted his power and defeated the Human Emperor power, those forces began to fear that Zhou Tian might actually win.
Therefore, taking those NPCs at that time as an example, they knew that if Zhou Tian won this battle, he might soon become unbeatable and potentially unify the world. So, regardless of how severely their own strength would be compromised, they saw it necessary to step in and block Zhou Tian's expansion.