Even more astonishing
It is, of course, all too easy to persuade oneself that one might have thought of X at the time: "hindsight is 20/20".
However, even bearing this principle in mind, it is breathtaking that the Malaysians failed to look carefully at their own primary radar recordings (civilian and military) around the place and time of loss of contact.
Similarly, as discussed at some length here earlier, civilian and military radar systems should have worked to make sense of each and every aircraft overflying peninsular Malaysia, including aircraft flying between established waypoints.
Either these basic steps were neglected over several days, or Malaysia's establishment balked at confronting the likely religious motivation behind a hijacking.