Shivas strongest ally was killed/sealed/punished right along side him, that being the Six Rings, the god of cyclic chaos. It's difficult to convey this, but the Six Rings, while still technically a separate entity, operate more like an organ to Shiva. Think of it as the relationship between a father and his child, a man and his dog, a warrior and his sword, or a body and its heart. They're tight like that.