Isn't that due to a different relationship to travel? Many on foot, villagers passing through from one area to another perhaps for the market, it makes sense that there will be more opportunities for "walk-in" accommodations. In the US the expectation would be someone flying or driving long distances, or perhaps taking a bus, but not to sell produce at the regional market on foot. And foreign travelers to the US are often people of some financial means or are operating in specialized systems geared towards immigrants, like some of the "mexican" coach services in some states.

I did find, like it seems you did, that I loved traveling through Nepal and the accommodations you've described. Remarkable and tough people living hard lives with resilient cheer.