It happens, but with limited effect and restricted to certain jurisdictions. My point is that the social web is not owned or controlled by any one commercial entity, just like the rest of the web.
The pirate bay is blocked by law in Norway by the ISPs DNS servers, but is trivial to get around. It is a very soft kind of censorship, which is the beauty of the Internet.
that's archive.ph's doing because they don't like cloudflare (there is a DNS extension where a DNS resolver forwards the prefix of the users IP to the DNS server of the site. Cloudflare does not use that, and archive.ph/.is says that they break their ability to properly host their site by doing that)
This is done more then you think. Probably the most known one is thepiratebay for example