Remnants of a strong weapon remained powerful even after it was broken into three parts. Additionally, the three parts attracted each other.
From the lowest level sea creatures, the three fragments wandered from one creature to another. Sometimes through peaceful means, sometimes through forceful methods.
The Realm Splitting Spear was originally used to soak in the blood of Li Guang's enemies, so it was constantly on the look for bloody confrontations to strengthen itself.
The unrest that it caused within the ocean posed a great disturbance to the Four Sea Kings who ruled over the entire water body in the human realm.
The Four Sea Kings did not want to have anything to do with a wretched, broken weapon. In the end, the fragments were carried by turtles to the dry land and dumped unceremoniously at a beach.