Your premise is obvious: They must have been in contact with someone who traveled. Your conclusion is not: The traveler must have been "illegal". In fact, you'

Your premise is obvious: They must have been in contact with someone who traveled. Your conclusion is not: The traveler must have been "illegal". In fact, you're almost certainly wrong. Furthermore, all travelers are not checked just for immigration status (you DO realize that tourism is a thing that is allowed, right?), but they were also checked (albeit poorly) for signs of infection in the travel phase. It's just not good enough. Many articles were pointing out how they weren't even using the temperature guns correctly, and infected people can be contagious for weeks before the signs even begin to show. Screening techniques, even if used perfectly, are inadequate. You'll never eat your words for what you're wrong about: the connection between illegal immigration and Covid-19, because you will convince yourself that your views are correct despite the fact that virtually no cases of this will ever have anything to do with illegal immigration.