>Because the US chemical industry has been effectively unregulated for a century and can do whatever it pleases.
And yet I bet if I look there's actually a ton of regulation.
>Chemical A is found to be cancerous
Chemical A is assumed to be cancerous by the state of California, you mean?
> And yet I bet if I look there's actually a ton of regulation.
I'll bet a ton of that regulation is insufficient, and/or paid for, or even written by, the industry to make it harder for competitors or to allow them to increase their profits by cutting corners.
Regulation isn't some on/off switch that always makes things better or worse. What matters is what those regulations are and who they serve.