Why are parts of the upper Mekong River valley remote and sparsely populated?

The upper Mekong River valley is remote and sparsely populated primarily due to its challenging physical geography. The river in this region cuts deeply into a rugged, mountainous landscape, creating a long, narrow valley characterized by steep slopes and relatively inaccessible terrain.12

As the river descends from the Plateau of Tibet through the highlands of Yunnan, the difficult topography limits human settlement and development. While there are historical caravan routes that cross the river, the overall environment remains isolated compared to the more densely populated lower basin, where the river flows through gentler plains and plateaus.12