User blog comment:Observer Supreme/918 Review and Thoughts/@comment-29325824-20180920134308/@comment-174.84.34.182-20180921012150

I think the best explanation is that the family had faked their deaths after Oden was murdered so as not being persued indefintely by Kaido and the shogun. They have since been trying to build up a rebellion to overtake the forces. Kaido and the shogun realized that they were still alive and started searching for them and the rebellion, resulting in those still alive to sail out to Zou for reinforcemetns. The cemetary is a reminder to those who remain that the old Wano is dead.