It *is* interesting that all these military air-surveillance radars and satellite-born radars and optical systems never have anything to say about planes that go down, at least in time to help S&R. AF-447 and MH-370 were a real disappointment in that regard.
It's a big planet, and much of this surveillance is focused on specific, mission critical bandwidths that don't necessarily include civilian aircraft hulls, to avoid data overload. It's impossible to see everything, everywhere, all of the time.