Dai Song Lan's reasons for hiding information from the rest of the Four Pillars in Shen Society was unknown for anyone save for himself. Perhaps he might have said it if Han Jing had asked it—but since the man failed to do so and was happy to accept money from him, then it was unnecessary.
He did not like speaking too much.
The black pearl in his hand was tiny and almost like a marble, but because it had come from the depths of the oceans, the concentration of the ocean's essence was supreme. He already made plans to purchase the rest that Han Jing was going to acquire from the Mermaid.
The city that both Dai Song Lan and Han Jing lived in already had its own fair share of troubles… and expanding to other creatures, or races, that certainly did not come to attack their jurisdiction meant that Song was more than alright to let it go.
Be wary of poking into things that were far too bigger than what one was.