We try! But most California restrictions on handguns have been struck down by the courts, and many of the surviving restrictions manufacturers simply refuse to comply with. They've been boycotting microstamping technology for over a decade, blatantly lying about commercial viability as an excuse for their policy preference not to do it. (I'm slightly sympathetic, because it is true that the first manufacturer to comply will probably themselves get boycotted by anti-gun-regulation zealots.)