No one government does not and never will completely controls the internet. In some countries child porn is actually legal.

If a site goes up it could be weeks or months before someone finds it. No one person controls every server. A site doesn't come up and an internet controller gets rid of it. It has to be reported and investigated. There is no way to stop something from getting on the internet if you cannot get control of a server that holds the information. I could put child porn on the internet and transfer it through a network to a private server. Someone would have to hack into a server and take it down. Usually what people do is they trace the server to the location and arrest the owners and shut down the server.

There are also many laws such as if the information or media is legal in one country another country has no right to get rid of it without consent from the country that the server is in. If you own a server you have basically free reign to put whatever you please.