The plane was shot down: This theory suggests that the plane was accidently shot down by US-Thai joint strike fighters in a military exercise in the South China Sea. This theory also claims that search and rescue efforts were deliberately sent in the wrong direction as part of a cover up.
Why don t they put trackers on planes?
GPS transmitters, such as are used by the police or by business vehicle fleets, need to be within range of a receiver. An aircraft at any kind of cruise altitude would perforce need out of range of such receivers.