Obtaining those things wasn't a simple task at all.
Zhou Tian had already obtained everything that was readily available. Now, if he wished to obtain more, he needed to use his skills or the resources at his disposal to trade for them. But, it was clear that any potential trades now could be compared to exchanging apples for oranges; from his point of view, such deals wouldn't bring enough benefit.
Therefore, if Zhou Tian wished to continue his collection mission, he would definitely need more experience. As for how to gain that experience, for Zhou Tian there weren't any other choices.
Though it was unclear if Zhou Tian or this organization had any interactions with NPCs, he was certain that there were no opportunities to target these NPCs or players. As such, Zhou Tian's only chance to gain experience was hunting and killing monsters in this organization.