Cost is a factor, but not really the dominant one.
In the midwest, the big deal is insulation. Wood-frame cavity walls are better at insulating than brick. 4 inches of brick has an r-value of .44 while 3/4 inch plywood uninsulated by itself is .93; try looking it up if you don't believe it. A typical modern wood frame exterior wall has an r-value of 12, when the air barrier, sheathing, air gaps, cavity insulation, etc. are all considered. Hence in the midwest, with the extreme continental weather, nobody builds in brick (although you'll see brick facade). As for tornado proofing, standard masonry is insufficient. Some people pay gobs of money for a single tornado proof room, which involves steel reinforced cinder-block construction; most people just dig a basement.
On the west coast, building code typically requires either steel frame or sheathed wood structure (wood frame covered entirely by plywood or oriented strand board). You do not want to be in or near a traditional masonry structure in an earthquake. Sheathed wood frame has far better quake resistance, and is considered highly survivable for high-magnitude quakes up to 3 stories tall without anything more than paying attention to making sure it is sheathed all the way around and tie down to the foundation & between floors.
That wood frame happens to be quite inexpensive is nice bonus, but not the whole reason.