Because in China when people start

Because in China when people start to question the Government the government cracks down. Opponents are called terrorists, traitors and unpatriotic.

The state controlled media that supports the government 100% then begins to feed the masses with all sorts of stories about how the government is good and only wants to help. That the dissidents, are a danger to the country because they question the wisdom of the government.

To make this stick they have to block outside sources of information because they fear that the people will not just accept the media stories and instead decide to find out the truth for themselves.