Personally I'm inclined to the "Helios" theory that that the crew became incapacitated in some way.
In other words, it's happened before and could happen again...hypoxia leading to confusion, unconsciousness and ultimately impact with the ground.
Having worked "on the ground" in various parts of Cambodia and Vietnam I am very aware that there are some extremely remote regions that are deeply forested. Just as an example, I was familiar with Ratanakiri province in eastern Cambodia.
It may sound unlikely, but at night, it could just be possible for a 777 to come down without being 'noticed'.
I don't know to what extent these areas are being searched?