Because what China's ban of US social media might say is that China recognizes social-media's power to influence the populace (think Russia's use of Twitter and FB in the 2016 election). Yeah, am actually in favor of some form of restrictions, because we as a country need to realize that social media is a tool that can be used against us.
Yeah, if it was an outside country owning a major US newspaper, it'd be more clearcut.