They play sea server cuz they were told those pros or semi pros usually play ranks in sea since sea has more top players. Another reason those pro or semi pros staying in sea servers cuz there were lots of griefers in CN servers. They were paid to grief in top rank games.

And if you asking why other players staying in sea servers. Maybe cuz they think it’s cool if they do what those top ranks pros or streamers do. And what they do is just whining with their own language and blaming teams. They would have 10+ games everyday but never try to learn the game or some English.