Basements are built for reasons. Comparing a 2-story house with no basement and a 1-story house with a basement, all things considered, the 2-story is cheaper. It costs a lot of money to dig down before you can build.
The only reason anyone has a basement is because they need one. In the northeast and midwest, where the whether gets much colder, you need to have a foundation below the frost line. At that point, you only need to dig a little deeper to have a full basement. Or you can stop and have a partial or look-out basement.
California houses simply do not need basements. The fact that there are potential earthquakes could be considered a reason, but since there isn't a reason to build them in the first place, it seems like an afterthought.
