Why would Japanese people move to CA for the more stable geology ?

Japan is one of the most seismically-active areas in the world.

As a result, [modern] Japanese construction is incredibly resilient.

I've never been in Tokyo, during a strong quake, but I'm told the skyscrapers wave around like drunken dancers.

It's a point of comparison to illustrate the differences. CA is seismically active, but not to the degree of Japan. Reading any further into it than that was clearly not the intent and would be foolish.

Because there are no longer any other good reasons to move here.