The claim is hooked rims on mountain bikes (and presumably gravel bikes) can result in tubeless pinch flats. I am not even sure that is a thing, but it is a bit of a flimsy excuse. I never heard of hooks weakening the rim. I think it is just easier/cheaper to manufacture a carbon rim without hooks. There don't appear to be many aluminum hookless rims for some reason...

For higher-pressure road tubeless applications, a case can be made that hookless rims are less safe, in terms of tires blowing off.

I think the "scam" part is claiming hookless is superior, especially for higher-pressure road applications. Enve has a (rather short) list of tires it regards as safe and compatible with its hookless rims. That does imply a very small margin of error.