How did so many untreated half-timber houses and log houses survive to modern times?

My grandparents on both sides, who were born around 1920, tell about how there used to be a lot more log houses on the landscape. Whereas ordinary timber houses survived, yeah. there is a dearth of the familiar log houses built over a century ago.

And, books about building log- and half-timber houses ALWAYS tell about necessary wood treatments.

But that aside, there ARE log houses around (and water mills, etc etc) and half-timber houses built in the mid 19th century to much before, that are still around. They may have been preserved from rot and insects starting fifty years ago, maybe, but how did they survive 100 years or more from rot, weathering, and termites?

Storage sheds built in the 1980s sometimes aren’t even around. How did log houses and half-timbered houses survive untreated for so many years?