Right now, nothing is happening in that mass grave, but that doesn't mean it will always remain stable. Once the Wind of Death spreads, a large number of Death's Claws will emerge from the ground, and then a multitude of zombies and skeletons will crawl out from the earth, beginning their revenge on the living.
Back then, the Hesse Territory suffered heavy casualties, and even their own people couldn't manage; there was no energy left to properly handle the remains of those monsters, leaving hidden dangers that it's now time to address.
Su Li does not want to wait for the future, when things mutate there or some disaster occurs, and then regret it too late.
He has always been inclined to prepare for the unexpected, to nip danger in the bud.
When this Shroud Order arrives, they will be able to excavate these remains and re-bury them, at least sending their restless souls to Mole's world.
