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.

People have been intentionally trained to have zero media literacy and propaganda works. You would think the elites would learn, seeing as teaching a population to uncritically ingest everything put in front of them is how we ended up with antiscience flatearth antivaccination sovereign citizens voting in the pedophilic reality show "star" who is actively destroying the world's economy. Greed has worped the ultra rich to the point they literally can't see anything further then how their own stock portfolios are doing right this moment. Fuck them. And fuck us too I guess because we let it happen.