California causes a large annoyance to supply chains and manufacturing. Their strict environmental standards mean as a trucker, you either service California or not. It's not something you just decide to do starting next week. From memory, the truck engine has to be under 10 years old and meet really strict emissions standards, costing a significant premium.
For manufacturers, ensuring those stickers are in anything sold in California is a pain, and when you make millions of units, it often doesn't make sense to just apply the sticker, labeling, and documentation to everything you make.
The environmental standards have a more tangible benefit and can have a pseudo-national effect given the size of California's market, so I'm not critical of that aspect. Slapping warning labels on everything without changing it feels like a waste of time, at least if you're not selective enough to make them useful to consumers.
For manufacturers, ensuring those stickers are in anything sold in California is a pain, and when you make millions of units, it often doesn't make sense to just apply the sticker, labeling, and documentation to everything you make.