How about this for a thought? People in a position in the Malaysian government to screw with the investigation and the radar were bought off or helped for personal reasons. The pilot was involved. That is all you really need. It is hard to steal a plane and get away with it, but it is not as hard to make a plane turn and avoid bought off radar coverage on a flight on a weekend during the middle of the night.
You then throw enough false leads out or misinformation to keep everyone focused on other things for a few days until it is too late to do anything. Remember how no one knew where to search the first few days. No other governments were willing to help and the big countries of the world were all caught up with Russia and Ukraine.
If a plane crashed or ditched in the sea, even if it stayed intact, which seems impossible, wouldn't something float to the surface or to shore?