The station manager is terrified of Kurtz because of Kurtz's known violent nature and because of the influence he seems to wield among the natives. To keep his station, the manager takes Kurtz's side, pretending that he is a great man and that he should be honored. However, when Kurtz is safely in restraint, and very ill, the manager confides to Marlow:
"...Mr. Kurtz has done more harm than good to the Company. He did not see the time was not ripe for vigorous action. Cautiously, cautiously—that's my principle. We must be cautious yet. The district is closed to us for a time."
(Conrad, Heart of Darkness, eNotes eText)
The manager's caution is what allows him to continue surviving in Africa, despite the bad conditions and dangers. He is concerned first and foremost with his own safety, and so he refuses to commit to any reckless or risky course of action. His basic method is to wait out any danger, while trying to ingratiate himself with anyone in power. In this manner, he continues to live as a coward, never taking a risk for himself, and letting others kill themselves in the jungle.
When Marlow first arrives, he discovers Kurtz is sick. The he also discovers the boat he is to take is grounded and need rivets. Marlow's trip to see Kurtz is delayed several times. Finally, as Marlow is leaving, he overhears a conversation between the station manager and his uncle. It seems the manager, who praised Kurtz to Marlow's face, really fears Kurtz's influence. The uncle replies that, hopefully, the climate will eventually beat Kurtz. The implication is that the manager has been delaying Marlow's voyage purposely to allow Kurtz to die without proper care.