Mining, transportation, processing stone in the mountains is a very difficult and huge project.
It's just like when we build a retaining wall, we flush out the flat side of the irregular stone, and then fill the gaps with mortar.
This reduces the enormous amount of labor involved in mining, transporting and, above all, processing the stone into the same size geometry.
The advantages are low cost, simple, and not nearly as strong as the result of regular stone construction.