The problem is that none of the default protocols work in China. Either they are blocked via DPI in combination with techniques like TCP RST injection / null-ro

The problem is that none of the default protocols work in China. Either they are blocked via DPI in combination with techniques like TCP RST injection / null-routing of the destination IPs, or they are known to be insecure, like PPTP (which is why it is removed in iOS 10)