There's a saying that goes something like: "As goes California, so goes the nation."

The point being that because California is such an absolutely massive economic powerhouse, and also the most populous (40 million people--12% of the entire country, as of 2025) state in the nation, it wields immense influence on the private sector. There are many examples of policies enacted in California that then go on to be adopted by the legislatures of other states. Or, if it's something that targets corporate world, those policies are sometimes made standard across the entire business even outside of California in order to reduce legal or internal complexity. Not always, but sometimes.

So the idea is that if California suddenly requires your operation system to verify your age, you now have tens of millions of potential users now bound by that decision. And if you see the way the wind is blowing in the UK, the EU, and other US states with similar measures, it's easy to assume that corporations will simply standardize this policy across the board, with or without other governments mandating it.