It used to be common sense among non-authoritarians, that propaganda just becomes more potent from suppression.

Plenty of people have never seen moon hoax theorists' propaganda. They imagine if they see it, they'll quickly see through it for its absurdity. But they're often wrong. Moon hoax theorist's propaganda is actually much better than you think. They can point out lots of "inconsistencies", which do have an explanation, but aren't immediately obvious at all. You see they have experience meeting people like you, but you don't have experience meeting people like them.

I used moon hoaxers as an example because their sophisticated propaganda actually have been exposed and explained a few times, although it still isn't common knowledge why e.g. it seems the exact same rock is right behind an astronaut in two different photos. But that isn't nearly as true for suppressed ideologies. You haven't heard their arguments.

Your example of moon landing theories isn't an apt comparison because you're picking a fringe group. RT already had millions of international followers on Facebook, YouTube, etc., often more than high quality journalism outlets. I've been online long enough to see RT showing up uninvited in my feeds before.

Consider the cost of the sites I listed. Literally, how do you pay these companies? With the monetization of your attention, first and foremost. Good journalism costs money to produce, leaving good journalists unable to be the highest bidder.