The goblins truly had too many character flaws.
Fearful and submissive, they were prone to feelings of envy.
The intensity of the NPCs' counterattacks had scared the goblins. Nowadays, they reluctant to fight back against the NPCs because Zhou Tian's situation was much better than theirs, leaving them feeling resentful. As a result, the goblins were unwilling to continue their desperate struggle against the NPCs.
Consequently, just as Zhou Tian had occupied several NPC castles, the goblins, dissatisfied with Zhou Tian's unequal benefits, promptly withdrew their forces.
The goblins' withdrawal led to the breakdown of their alliance with Zhou Tian. The crisis that could once have posed a fatal threat to the NPC side had thus quietly passed.