That's what the website says. In every other state, they can recommend Mercon V. California is the only state which says, "no". Why? "Viscometrics" do not match OEM spec.
You decide for yourself. Valvoline recommends it, despite the fact that the fluid does not meet spec. Valvoline Multi-Vehicle ATF is not a licensed product for anything. Some brands will claim that their product is compatible with certain specs. Other brands are licensed. Lots of controversy regarding the "license". Some people believe that it's the only way to tell if that product is to spec. Others believe that it's simply a way for OEMs to make more money, by making money off someone else's product. Sure, an unlicensed product could be just as good, if not better, than Mercon V, and that bottler just does not want to pay GM or Ford for their Dexron & Mercon licenses. No way for you to know, other than to trust whomever is selling you the product. From my memory, Royal Purple, Red Line, Lucas Oil......all sell ATF, without a Mercon license. All the nationwide lube shops use multi-vehicle ATF, and somehow, those cars are not blowing up transmissions.
49 states don't care; because the old rule of thumb is "let the buyer beware".
California is a "nanny state". California thinks that the consumer is too stupid to research the product themselves, see on the label where it says "recommends", but there is nothing to indicate licensing, or to even be smart enough to read the label since the current retail bottle label makes no mention of Mercon V at all.
You decide for yourself, when you go to the store, and see which formulation or bottling batch is on the shelf. I just picked up a bottle. It no longer says Mercon V on the bottle label.