There are many tools that might be used to create a biological weapon or something. You can use a pocket calculator for that. But we don't place bars on sale of pocket calculators to require proof be issued that nothing hazardous can be done with them. That is, this is a bar that is substantially higher than exists for any other tool.
Second, while I certainly think that there are legitimate existential risks, we are not looking at a near-term one. OpenAI or whoever isn't going to be producing something human-level any time soon. Like, Stable Diffusion, a tool used to generate images, would fall under this. It's very questionable that it, however, would be terribly useful in doing anything dangerous.
California putting a restriction like that in place, absent some kind of global restriction, won't stop development of models. It just ensures that it'll happen outside California. Like, it'll have a negative economic impact on California, maybe, but it's not going to have a globally-restrictive impact.