One other note is that there's a difference between existence of a law against something, and enforcement of that law.
Let's suppose, for the sake of argument, that some company is falsely advertising such a product, in violation of state false advertising law. Who is actually going to stop and/or punish them?
The state prosecutor / attorney general / consumer protection agency might have the power to order them to stop, or to fine them. But they might well decide, exercising their prosecutorial discretion, that it is not the best use of their time and funds to go after this product. After all, the consumers that would be protected are people who are trying to break the law (and failing, since the products don't work), and the state might rather focus on protecting law-abiding consumers. They might also consider that if they force these products off the market, consumers will look on the "black market" and might find products that actually do work.
Individual consumers might also have the right to sue for false advertising. But in order to do that, the consumer is probably going to have to testify, under oath, that they were attempting to obtain a product that really would block photos, which would be illegal. Incriminating yourself under oath is not a great legal strategy. Anyway, these products are usually pretty cheap, and likely no individual consumer would find it worth the expense of going to court.
So it could be that the companies are breaking the law, but nobody has an incentive to enforce that law against them. Thus they can just keep on doing it.