It probably took generations to arrive at the optimum wall thickness.
https://en.wikipedia.org/wiki/Cob_(material)#Modern_cob_buil...
http://www.sotaconstruction.com/project_details.asp?id=42
Even mud hut technology has advanced well beyond huts. The "greenest building in Pennsylvania" is a glorified mud hut with underfloor heating. It contains more than just one century of advancements over the most basic earthen construction.
And perhaps you haven't seen the sort of houses that people lived in, even as late as the 1930s, in some parts of the country. Let's just say there is a good reason why pre-manufactured homes are popular in certain places. Upstate New York may not exactly be a representative sample for the housing conditions in 1915.
I don't think a mud hut was ever considered acceptable in any moderately advanced country back in 1915.