Well, for one, people have heard of that term. In North Korea, not many people identify as gay, partially because of the huge stigma but more so because most North Koreans haven't even HEARD of homosexuality. The same was historically true for trans folks.
Also, if there is less of a stigma attached to something, people are more willing to come out as that thing, and to accept that they are that thing. It's like autism - the reason there are higher rates of it isn't that there's something causing more autism, but that we have more awareness of it culturally and better diagnosing procedures medically.