disproving bullshit is a waste of time because nobody is meant to believe it.
Okay, but why does it continue to work so well? I think lots of people do believe it, or believe it "might" be true. I run into the believers and semi-believers often when I'm otherwise happily commenting around the internet. As a typical example consider this comment ranked 5 from Anonymous Coward:
Newsflash - the intelligence agencies of the United States have a documented history of breaking the law.
Any claims based on the assertion that they behave lawfully is flawed and not to be considered credible.
This style of thinking - and there's a lot of it - allows any layman to use a chain of reasoning like this: "so what if Trump's a bullshit artist? So is everyone else, therefore we can't tell who's right, therefore Trump may be right and I'm going to continue to stand by him."
Such arguments help establish the Russian model of propaganda in the U.S. Now, while the tactic of sewing doubt about what's true and false is well known as a Russian strategy ("therefore Putin may be right and I'm going to continue to stand by him"), I think in the U.S. the dominant cause is that the conservative media waged a war on the credibility of the mainstream media and won - as described by this conservative publication.