This is just a wild guess on my part. I have not spent a penny in research money to come to this conclusion. It just could be that this group of people are engaging in a behavior that is unique to this particular population, and that behavior is putting them at vastly increased risk of contracting syphilis and HIV. Since these are both venereal diseases, I conclude that these people are engaging in sexual practices that are different that the rest of the population.
There are those who provide details which i will not, as well as biological differences btwn the two “ports” at issue.