The world powers rarely enter the Turbulent Sea because it is hard to maintain control here. There is too many force here to pacify.
There are the warlords. Then there are also the pirates and the Crime Alliance and a dozen more outlaw organization that fled to sea after the Multiversal Convergence.
Most of them fled to this sea because the eyes of heaven could not see through it.
The warlords, the pirates, these outlaws and criminals are all unruly and hard to control.
To many of the Great Powers, they simply do not represent profitable investment. And there is a lot on the plate of the Great Powers
It is hard to say whether Death Monarch was unlucky or lucky when he came out of the portal and end up in the Turbulent Sea.
In hindsight now, Death Monarch was lucky. Arthur submit to him and now Pandemonium has a force in one of the Ten Seas.