Because the FDA has very specific rules as to what constitutes medical advice and what doesn't. The claim of "helps you sleep" is not medical advice and not regulated.

It's the reason so many "nutrition" companies can get away with claiming all kinds of things such as "burn fat faster". That statement means something to you and I, but it's not a medical statement.

The comment I was replying to said the claims had no meaning, not referring to the FDA.

They might be "meaningless" to actual medical professionals or people with decent knowledge of the ways that companies skirt product labelling laws. But the average layperson who might buy these products is probably neither of those things and is more likely to interpret them literally.

Because if the products actually worked they'd be allowed to claim they work for actual diagnoses (e.g. "Fixes Insomnia from dose 4" vs "Promotes sleep")

I agree with the other two replies, but I wanted to add: the claim is going to be the strongest they think they can get away with. If they’re not making specific claims about specific outcomes, that implies they know they can’t get away with it. And, if they could make those claims, it would no longer be a “supplement,” but a “drug.”