This is costing the Chinese massively in Satellite resources.
Photo reconnaissance satellites typically follow a polar orbit. This goes over both poles, whilst the earth rotates underneath, so they spend equal amounts of time in the northern and southern hemispheres.
The timing of the orbits puts them over their targets early in the morning or late in the afternoon, in sun synchronous orbits, to get 3D perspective.
To change orbit to look at a different target uses up manoeuvre fuel. They obviously only have a finite amount of this so using it is incredibly expensive in terms of the life of the satellite. They also use fuel to counter the effects of orbital decay.
During the Falklands war the USA changed the orbit of a KH-11 (which cost well over a billion dollars, more than a Nimitz-class aircraft carrier) to provide the UK with intelligence. Casber Weinberger earned his knighthood.
When the Chinese moved as many as "10" satellites to the Gulf of Thailand/South China Sea it must have cost them an utter fortune in using up the life of these assets.
When they changed the orbits again to cover the southern Indian Ocean it cost them yet another utter fortune.
They will now have a very big shortfall in their reconnaissance capabilities for a few years as they have to manufacture new resources.
These satellites have many sensors, not just the visible spectrum. Use your imagination a bit and they will have tried it. KH-12s weigh about 20,000 kg, which is a huge amount of kit. And they are not the biggest.
They produce immense amounts of data, far more than could possibly be analysed by humans. So the initial analysis is done by computers, unless they are examining a known target.
All this means that they can look at a lot of the sea and can examine it in surprising detail. If you just think of what they have already found it is needle in a haystack stuff.