Most Fediverse users are Western. The Western world has plenty of media diversity, and you can find virtually every viewpoint you can imagine represented there. Open criticism of government, all the way to the top, is a normal part of everyday life, and media outlets regularly criticise each other, and themselves, for bad takes and poor journalism.
Because of the diversity of media opinion, it is harder to push an agenda, so mainstream Western media does it, by and large, with substantial subtlety, building trust first, and seeding ideas over long periods of time.
Russian and Chinese media aimed at a Western audience seems brash and full of bad takes by comparison. It is rarely, if ever, critical of itself or of its own government, and also rarely provides any independently verifiable evidence for its claims. To a Western audience used to Western media, it appears so one-sided that it is laughable. That is why it is easy for people in the West to dismiss it as propaganda.
You could probably write a PhD thesis on why media outlets in China and Russia find it difficult to play the Western media game, but I think the main issue is this: If you live in a society that doesn’t itself value diversity of opinion and thought, it is difficult to produce media for a society that does value that without it seeming off-kilter. It’s a bit like the difference between being fluent in another language and “feeling” the language. To a native speaker listening to it, the difference is really obvious.