I appreciate that's literally the first site that comes up when you DDG "why are us houses made of wood" but it's credibility is... lacking (and I'll confess, I'm quite content having an answer that differs from the one given on an AI generated slop site.)

Anyways: I can't exactly agree with the idea that the entire US west coast is a "very small portion" of the country (being the 5 pacific states alone account for ~1/7 the population and ~1/5 the land mass, and the geologic "hot zone" that's relevant here extends much further east than those 5 alone). I recommend reading ASCE-7's section on seismic design (IEBC codes are much easier to obtain, but unfortunately also much less helpful) if you ever are having problems falling asleep / for further specific information about this topic and the performance of unreinforced and seismic retrofitted unreinforced masonry vs. wood construction in an earthquake. The prevalence of unreinforced masonry buildings in the east coast vs. west is without a doubt in no small part down to the availability of materials, but as is usual, treating the US as homogeneous is generally a recipe for unhelpful statistics. To illustrate some of the historical reasons as to why there are differences in building materials between the western and eastern US:

This image (source) is a charting of every 4.0+ earthquake in the lower 48 (4.0 being the general threshold at which seismically unreinforced (old) masonry buildings begin to sustain damage) for the past 125 years. You may be able to notice the little section labeled "Milwaukee" that is completely devoid of any big gray circle - I suggest that just perhaps this is a factor in the initial adoption and subsequent length of popularity of brick construction in that region, which from what I am reading appears to have continued a full 50-60 years after similar construction went out of popularity (or was outright not permitted) on the west coast. Certainly the availability of timber over brick in the regions was an important factor, but there the motivation for moving away from brick and stone was much more of an economic one, as there were few more complex motivating factors (like "the ground is trying to kill me" (instead the air frequently tries to kill you - an event that brick and stone are far more useful in combating)). There was ample unreinforced masonry construction in the west in the 1800s - 1900s, but for some unknowable reason there are very few examples of that construction remaining in the modern era...

I'm not saying economic pressures aren't a factor, but "will the building will fall down and smoosh me" (or sink into the swamp, or have it's foundation eroded away, or...) is similarly critical factor to consider.