In these difficult times, if the Lu family were willing to speak up, the Wang family might still be able to preserve some of their assets.
Even if other forces were to devour the Wang family, with the Lu family around, they would still give some face and spare the Wang family.
If the three elders of the Lu family hadn't died because of this incident, Lu Bo wouldn't have minded taking over some of the Wang family's businesses and sparing them.
After all, when you take from others, you owe them a favor.