Why is there no freedom of the press in some countries ?

In democratic countries, journalists are free to investigate and publish any information they want. They also have the right not to reveal their source. They can criticize the government without fear of reprisal. The only limit: they can’t accuse someone without proof (that’s libel) or incite racial hatred against part of the population. If someone is not happy with what the media are saying about them, they can sue them. The judge then decides if the media are right or wrong. 

But freedom of the press does not exist in all countries.

In authoritarian states, such as North Korea or China, the government uses censure: newspapers can only publish what is allowed. Any journalist who breaks this rule can end up in prison… or worse: in some countries, journalists are killed because they upset those in power or their friends. Governments justify limiting the freedom of the press by saying “state security depends on it”. In fact, they are really afraid people will turn against them. Dictatorships also limit or forbid access to the Internet, because foreign news articles can be found there. And people who are well-informed by a free and independent press are much more difficult to control.