Why is this attitude being taken by the investigators? It almost sounds as if they are not willing to try too hard.
I suspect that they are trying to keep expectations low, as there is a fairly good chance he may be right. If they are actually found, they will look like heroes.
Based on the history of these types of incidents, searchers have been able to find the recorders in circumstances that seem equally difficult more often than not. They also want to find the recorders, since if another similar unexplained incident happens, it would wipe out orders not only for the A330, but also for the A350 and any chance at keeping the tanker program. (Think deHaviland Comet)