Misinformation is a numbers game. For every 10 people that see the misinfo, only maybe 1 or 2 will ever see the followup proving whatever the misinformation was was in fact misinformation. And out of those 2, half will assume the followup is itself misinformation and have their belief in the propaganda reinforced. Out of the 8 who will never see the correction, maybe two will reject it, four won’t really know what to think (itself a useful propaganda outcome), and maybe two will accept it.
Concerted efforts to combat misinformation can help, maybe nowadays the number of people who see the followup is closer to 3 or 4, but it’s the same basic dynamics behind the Gish Gallop, but on an industrial scale. Making up bullshit is easy, analyzing and explaining why it’s bullshit on average takes longer than spewing out some new piece of bullshit.