>we got our own celebrities and a way to talk about them
Maybe, but Gul Dukat isn't a celebrity, he's a character. The study isn't asking people about <character from currently popular movie or TV show>, but about real, living celebrities. If they asked about the #1 character in Bridgerton, whoever that is, that I think would be comparable.
It also doesn't help that they're mainly asking about current celebrities. A 60-year-old doesn't give a shit about the Kardashians or Justin Bieber. Obama probably. But some celebrity who was big 30-40 years ago would be of much more interest to them.