I’m not sure it’s legal to call them candy cigarettes though - I’ve always seen them called something else. Yup, it’s illegal to call them cigarettes in the US, and they vary in legality elsewhere.

I only ever see them for sale in places that sell old fashioned candy, I think their decline has to do with the fact they just don’t taste very good (in addition to the changing cultural opinions about cigarettes, but I bet they’ve declined even in places where a large percentage of adults still smoke).