If you don't have any glass - or simply cannot afford it, it's expensive in a remote place like this - and don't particularly need incoming daylight either (maybe because it's just a storage room), boarding the windows up is of course a much sturdier solution than mounting a plastic sheet.
The problem is that wood is also expensive: at nearly 4000m above sea level this is above the tree line, and wood would have to be "imported" from far away over a road that here and there hardly deserves the name. All materials that could possibly be reusable as building materials are carefully preserved (not just wood). Here, the former windows have been boarded up with a variety of old planks, carefully arranged to make optimum use of what's available with the least amount of waste: this way, the wood can easily be reused again should the need arise.
The ladder tells another story: houses are built with flat roofs here: they serve as storage area for things like dried dung (for fuel), tools, and (yes!) stuff that one day might be reusable. The ladder is the only way to get up on the roof.