Earlier quoted context omitted.
Once a contractor told me my apartment building, which was built in 1939, has very good load bearing walls that "they don't do nowadays". I do think that it could be more of "nowadays we can use lighter material to do the same job" angle. I also vosited quite a few apartments where they used thinner material and sound proofing is not exactly great.
Couldn’t this just be survivorship bias? We already locked down all the cheap crap from the 60s. It’s only the rare, well-built buildings that are still around. We’re building more cheap crap, sure, but also a few rare, well-built buildings.
Here's a page showing some of those mail order catalogs: https://www.thoughtco.com/foursquare-house-plans-catalog-fav...
Looking from the basement up through to the framing, or from the second story down to the flooring, EVERYTHING was built from really thick timber. If you've walked around a modern unfinished project you can see nearly everything wood is made from fast growing wood or particles of wood just glued together. And that holds true even for "high-end" home projects (aka homes sold as high end because they have fancy kitchen appliances, not solid construction).