This plan of Huyan Clan's clan leader, Huyan Ba, was a long term one. Although Wu Clan had thoroughly deteriorated now, it still would not be an overnight feat to completely uproot it.
One must know that Wu Clan used to be the greatest clan in Yulong Mainland thousands of years ago. It was even more difficult to exterminate Wu Clan than Murong Clan!
The reason Huyan Ba did not dare act recklessly was simple as well. Murong Clan was annihilated! He felt that it was definitely not Wu Clan's doing and he did not believe that Wu Clan's Wizard Lord Wu would return.
There was only one explanation to the massacre of Murong Clan then. Wu Clan had most probably joined forces with a certain prominent clan and had wiped out Murong Clan directly.
This meant that Wu Clan had a strong support of assistance behind it. That was why Huyan Ba decided to go about the plan with further consideration and discussion to slowly wipe out Wu Clan from the root!