The problem is that it suppresses the majority of ordinary people but the people who actually want to do the stuff the government is trying to stop can still keep doing it anyway.
> Btw, censoring of keywords and blocking of websites are two different issues. VPN solves the latter, not the former.
So in China, they block access to foreign apps like Twitter, Facebook and so on, and so people gravitate towards the home grown alternatives - which are required by government to censor keywords and content.
Also, China does dynamic blocking of websites based on keywords and other things.
It's both very sophisticated and trivial to bypass.