From what I understand, the theory is that the route was specifically designed so that nobody would have known where it went. No evidence, no crime. By just nose-diving, it makes it easier to find that evidence (like the black boxes).

At the time, not a lot of pilots knew about the feature of the satellite communication unit that would allow investigators to estimate a track over the southern Indian Ocean. Without that, nobody would have known where the plane went after it left military radar range.

But why? To keep the life insurance?