Aksai also made a mental note not to visit the Purple Poison Marshland.
This region was filled with inherent dangers from vicious and poisonous demon beasts, and plants.
A dense amount of purple poison mist and water covered various parts of the region. In fact, it was said that the Purple Poison Marshland was the reason why the Purple River was purple and slightly poisonous in nature.
If the Lakir family had retreated to this region, it was understandable that not even the Foundation Building Experts would pursue them recklessly.
Aksai could also guess that the Lakir family always had an exit strategy lined up in the Purple Poison Marshland in case their demonic practices were made public. It was very dangerous for Aksai to even get near the region by mistake.
Why don't bone fiends fight each other? Because they don't have the guts! ;)