Someone asked why focused search near extreme end of the arc. I would say because this location fits with two hypotheses. 1. A deliberate plan to make the plane as hard to find as possible 2. Some mechanical problem and then the plane flew with autopilot until fuel exhausted (seems unlikely to me, but the location they are searching is consistent with this hypothesis).. Anywhere short of this location is arbitrary. It is also possible the pings were detected by a 2nd satellite, which would considerably narrow down the arcs.
We have been told that primary radar tracked something in the middle of the night. This was without any advance notice ie they did not really know what was happening. By the time if the last ping, it was morning and they knew they had a big problem. Every primary radar would have been looking hard. Surely this is the reason the central part of the arc was discounted. Could possibly be because the Pacific satellite didn't see the pings, but as Ana explained there are other reasons why pacific may not have seen. Indian seeing is more reliable than pacific not seeing. So I suspect more likely this area was discounted because they had lots of primary radar looking by time of last ping.
Still don't buy the theft theory. Too many variables, need other people involved, and probably couldn't set it up by the time you knew you had valuable cargo.
The only explanation making sense is that of someone who wanted to die, but wanted to disappear and for the world to never know where or why or how. Internally this individual was very rational - could not have managed this if irrational. But incomprehensible to others. There have been plenty of these throughout history.