Bad leadership in the political ranks. The problems that California has has hurt it for many years. We just have been able to get away with it due to tech and entertainment money largesse.

The progressive wing is against desalination plants and dams. They say that they are anti environment. They push for conservation.

The problem is that since 80% of the water is used by agriculture all the conservation efforts won't be enough. You can't reapportion the water because of water rights. The agricultural interests won't give up theirs.

Thus you end up doing nothing much and hoping for rainy seasons.

Other longstanding California issues: wildfires, insufficent power generation, bad schools, expensive housing.