They learn the tactic from their master the US. In Vietnam war, South Vietnam government propagated similar bad news about the North, like "Viet Cong" soldiers were so thin that 07 soldiers were not heavy enough to break a papaya branch. The South Vietnamese people were very surprised after 30 Apr 1975 finding that the North soldiers were just normal and healthy.
The West has been using their huge propaganda machines to bad-mouth their adversaries and enemies and brainwash their own people. However, thank to Internet, people now worldwide can easily see the chaos of the US and the savage of American people, the deep poverty in post-war "democracies" Libya and Iraq or the abject poverty and filthy in the over-hyped "world's largest democracy".
I used to hate communism. But the more I read and see, the more countries I have been to, the more I can see its superiority over Western-style liberal democracy. A combination of limited democracy and market economy with some state intervention may be the best option for most poorer countries now.