Because California is one of the most corrupt states in the union. Unironically. Socially they're fairly progressive, but economically they're essentially three mafias in a trenchcoat pretending to be a carnival owner.

Take the high speed rail project. Or how they have implemented cannabis licensing, or the ridiculously bad infrastructure and homeless resolution spending problems.

The day-to-day in California is shit for the average person, and they've now been told they are the most left-wing state for decades because of some social issues; so they're associating the shitty life they are living with left wing economics, despite pretty much no left-wing economics being involved. Populist propaganda works because you are correctly recognizing the problems involved, regardless of whatever solution you're selling -- and more "left wing" (aka neoliberal/conservative gay-accepting) candidates are essentially unelectable and objectively not the solution. Unfortunately the DNC refuses to run anyone remotely left wing in the entirety of California.