China is doing this because they are very quickly going to roll out their own system and they don't want the competition and their big enough that they will get away with it. Does anyone really think that China is going to allow its people to have anonymity in their transactions, that's like say the USA hasn't corrupted the whole money system. Power corrupts and absolute power corrupts absolutely.
In the very near future China is going to be the new financial super power and these cryptocurrency's are a threat to that. It's all ready working Bitcoin has fallen 300 bucks since China made this statement.