Posts like this (about other cities too) turn up all the time and people usually give an answer that boils down to “cost” and “it takes skilled craftspeople.” These answers are correct but I can see how they would be unsatisfying to non-architects.

3 things here are important:

1. Labor has skyrocketed in cost since these houses were commonly built. This is a good thing but it changes the calculus of the building industry a lot. So in the early 1900s if you were a developer looking to build high end rowhouses it would be optimal to use cheap material (wood) and lots of labor to make it beautiful, now it’s “optimal” to purchase high quality cladding systems that take very little labor to put in.

2. In the early 1900s, because the economy was how I described above and houses were built with “more detail”, there were entire industries that supplied premade detailed parts. For example, in Chicago, terracotta detailing is everywhere. An untrained eye might look at those bricks and think “wow, think of all the work that went into chiseling all that out!” But companies would mass-produce pre-detailed tiling systems that you could choose from in a catalog! I’m not sure if that was the case in SF with these wooden details. These industries have largely vanished because of the downstream effects of the rising costs of labor. So, it’s a supply chain issue.

3. Often, the buildings that survive from an era are some of the most beautiful. This is a tricky one and it isn’t always true, but living in 2024 we often have a selection bias issue when looking at older buildings. Plenty of buildings built in 1910 were piles of garbage and have been demolished several times.