This is an American website. The lady that owns it lives in Missouri. Obviously she's going to market to English speakers in her home country before she branches out internationally. Websites survive on advertising dollars, and advertising companies in America that will pay her, don't typically market to Chinese people. I'm sure she's happy to get what ever trafic she can get, but it's not like man I need more Chinese people on my site.
Language could be barrier. Also in many countries girls aren't allowed to date or worse have sex before marriage. Hence no need for GAG. But 80% being American is stretching it, plenty of people from other countries.