Kun Yun said that the rate that the crack of creation, which would complete the God World's laws, opened up at would be rather slow. Despite that, dense god spiritual energy seeped out from the crack and cultivating near it would allow one to gain insights into laws with extreme clarity.
Precisely because of these many cultivators of various races crowded around the crack - every single one cultivating without exception. In his heart, Mo Wuji was thinking about setting up a sect as Kun Yun had suggested, so he didn't want to stay here to cultivate. With the resources he required to cultivate, a few hundred years by the side of the crack might not even help him enter the peak of God Monarch Stage.
Moreover, it was as Kun Yun had mentioned. Although a crack of creation had appeared, it would take at least a few decades to a few hundred years before the actual explosion happened.