Why did settlers build sod houses?

They built their houses out of sod because trees were scarce in the Great Plains, but the houses also were convenient... however, they were dirty and brought snakes, insects, and (of course) sod. Also, in bad weather, rain could leak through the roof, and sometimes even bring the whole roof down on the family. A sod house also was vulnerable to fires and hail, and could cause conflicts in those conditions.