Because there exists a real, nonzero chance that this is the piece of evidence that will convince some of his followers to finally admit he is either insane, shockingly stupid, or incompetent due to dementia.
Main reason is that reality doesn't seem to concern the voter base of these people like Trump. If it did, we wouldn't be in this situation in the first place. And I'm not just meaning Trump here, but all the other populist leaders in the world as well.
I think if these kinds of articles were effective in that regard, we wouldn't be in this situation in the first place. So, if the goal is to change the minds of people for the better, instead of banging on about the trivial, we should be looking at how to communicate better. "Told you so" doesn't work.