Almost nobody ever gets earthquake insurance. It's one of those things that insurance companies don't like to insure, so they set the rates far beyond affordability. It's odd, given that strong earthquakes are an extremely rare probability event, and damage or injury from them is practically statistically undetectable. People who don't live in CA tend to over-dramatize earthquakes. I've lived here for 47 years, and have only felt 3 quakes.
It may be rare statistically for any individual, at least for catastrophic damage, but when it does hit, it's a lot of high dollar claims. It may just be that reinsurance dollars are only out there at a premium to cover the gap between claims and the insurance pool.