Populations are mainly local tribes with little of no communications with the outside world.
I've traveled by motorbike all over Thailand, Malaysia, Vietnam, Cambodia, and Laos, and this characterization simply doesn't hold true.
Even in the smallest villages, there is electrification of one kind or another, and someone always has a dish and a TV, often communally shared. While Laos and Cambodia are probably the least connected, I stayed at only one or two villages, high in the mountains that didn't have communications of some sort.
True, there is plenty of open space and rain forest. But, there are also many. many tiny villages interspersed throughout the rain forest such that it is difficult to imagine that an aircraft crashing at night would not have been seen by someone.