It could be that the batteries have finally died.
This means that the submersible gas an area about the size of Houston to search. This will take a while to do.
If they pick up the signal again, then the area will be dramatically refined.
Also, the submersible will need to deploy to look at the Chinese coords as well. Maybe they should deploy a second submersible.
Now if both prove to be false positives, then this search will go on for years and will cost Billions.