Either they are testing our capabilities, trying to distract us from something else, or there is something (or someone)else pinging out there.

Your other comments are spot on, though. They are selling us the rope, but I suspect they are finding it so profitable they may wind up hanging themselves with it too.

Just a WAG:

That plane was going to China, with mostly Chinese passengers aboard. Suppose there was something aboard, some cargo, luggage, perhaps even a document or flash drive, they didn't want anyone to know was aboard. It might not necessarily be some big military secret or intelligence thing... maybe just a little industrial espionage. Having it examined by experts might be very embarrassing.

Maybe they don't want the wreckage to be found.