The question I think is the right one. But the gov’t in question would have to be able to get the plane there without detection by others. The main reason I think it is in the ocean. Too much snoopery available nowadays.
By the time the plane's trail is located (looking in the wrong places), it could be in different paint and have been moved, even painted to look like a lesser aircraft from above (optical illusion). Then it could be hidden in plain sight, well, from above, anyway.