There's a nonzero chance military intelligence agencies of multiple countries know exactly where that plane fell, but none can say anything, because that would reveal the true extent of their capabilities.

Just like it was with that amateur sub that imploded. It later surfaced the Navy heard the implosion and knew what it was.

They could just feed the data to some associated outside party with some other plausible explanation. But, there are only a few, maybe two countries, with the ability and desire to have listening stations all over the ocean, and neither one is particularly interested in the Indian ocean.