My last house was built in ~1936. It was cheap for the time, but the entire estate of houses it sat in was complete - virtually nothing had been removed. The form of the buildings had changed somewhat (extension for bathroom instead of toilet in the garden), but the brick walls were incredible and the internal timberwork (joists, frames, etc.) was all hardwood of a quality that would be very expensive now.
My current house was built in ~1985. The brick quality isn't bad, the walls are much straighter, but the wood is cheaper and the materials thinner and lighter. It might be the case this place will last 100 years, but I wouldn't bet on it. It's a middle market house, for the time, not cheap but not high end.
While survivor bias is important, where I live (London) the main reason houses from 100 years ago aren't around now is simply the war. The stuff from then that's still about - including "cheap" factories and other stuff - is now wildly fashionable and still well-built. Stuff built in the 50s was laughably awful and a lot is gone, stuff from 60s and 70s is going the same way. There are definitely other things going on.
My current house was built in ~1985. The brick quality isn't bad, the walls are much straighter, but the wood is cheaper and the materials thinner and lighter. It might be the case this place will last 100 years, but I wouldn't bet on it. It's a middle market house, for the time, not cheap but not high end.
While survivor bias is important, where I live (London) the main reason houses from 100 years ago aren't around now is simply the war. The stuff from then that's still about - including "cheap" factories and other stuff - is now wildly fashionable and still well-built. Stuff built in the 50s was laughably awful and a lot is gone, stuff from 60s and 70s is going the same way. There are definitely other things going on.