Actually some of the players have MC online account but they didn’t use it because I set the server online-mode off. The reason is just as YangYe said, most of Chinese users cannot buy the International Minecraft account now and the Chinese Minecraft Proxy is not good to play with.
I don’t mean to offend Mojang but this is indeed an already existed and lasting problem. If I open the online-mode I imagine there will be only 20% players left.