I too owned a house built in the late 19th century with an addition built probably around the same time! The houses in the neighborhood were built to house workers from the steel mills nearby. On the main streets you had the foreman houses. Lots of brick, well made. My house was a worker's house, a stick frame shotgun shack. What little of a foundation it had was a few rows of bricks set upon railroad ties just below the surface. Most likely the only reason it is still standing is because it is on top of a hill and the soil drains quickly. When the wind would blow real hard the house would lean enough that the front door would open. The latch could get past the jam. Fixed it with shims but you get the idea. Nowadays building code would require a foundation built on footers beneath the frost line. (4 feet here) Another building code that is a big improvement is requiring (I forget the proper name) walls to be built in such a way that the space in-between studs doesn't act like a chimney in case of a fire. Major safety improvement there. I now own a house at least a hundred years old. Same story, built to house quarry workers. Fortunately someone who owned this house before me poured a concrete foundation all the way around. The additions on both my houses are pretty amateur probably because they were done by the homeowners and there was little enforcement of building codes if there were any.

Also well built houses also fall into ruin due to disrepair. Here in Cleveland there used to be Millionair's Row. A street where the titans of industry built their mansions, the Rockefellers, Carnegie, Mellon. Very few still exist due to being expensive to maintain. I have a lot of experience with old buildings not only in my personal life but also at work (I'm a contractor) also most of my friends are in the trades with experience in old homes. Suffice to say just because a house is old is no indication of its quality. I can saw plenty of bad stuff about new houses too.

Specifically light framing which was pioneered in the early 20th century and became the dominant construction method in North America during the post-war housing boom.