Mongolia is huge. Similar to the size of West Europe, and the population is only three million people (of which most live in Ulaan Baatar).
I think that the main reason for the low population density is the difficulty in growing food. Large parts of the country is desert or semidesert. The rainfall is low ( Therefore, the tomatoes don’t really like it here.
On the other hand, what you can eat here is meat. Grazing animals like sheep, cattle, goats, camels and horses are the five livestock pillars of the Mongolian society. Since the grasslands are sparse, the people move with their livestock across the plains and the rolling mountains.
We visited a modern nomadic family an hour drive outside of Ulaan Baatar.