I am not sure, but my guess is that the packaging is not compliant with proposition 65. California has a variety of regulations which force small changes to packaging and manuals.

It's probably because they don't meet some California environmental regulation (like energy efficiency or toxic chemicals) or aren't certified to meet those regulations. California tends to have the strictest environmental regulations.

Some models of cars are unable to be sold here for the same reason, although most are designed to conform to California regulations due to the manufacturers not wanting to miss out on the California market.