Why is there no clear national boundary between China waters and Japanese waters?

The above is too complicated. Let me briefly say that China and Japan have different ways to demarcate the middle waters. China sets the scope of territorial sea management according to the extension of continental shelf, while Japan takes the median line as the maritime boundary. Both demarcation methods are based on national interests and are internationally recognized. However, the use of two demarcation methods for a sea area will inevitably lead to overlapping management. In addition, oil reserves have been discovered in this area. Of course, no one wants to give up, so the issue of demarcation has been shelved.