Why do people excuse Trumpian inventions?

Of course, so many words have been written already on Trump's intensely narcissistic and offensive comment on Rob Reiner's death.   There were few who tried to support it, but in the local scene I saw that old JC at New Catallaxy, who I think occasionally might come here, refused to condemn it because Reiner had promoted the "Russia conspiracy" and been mean to Trump, so Trump could be mean in response (even in death.)

Even ignoring the fact that JC is part of the intense stupidity that has engulfed MAGA world that refuses to believe the reports of bipartisan committees on the involvement of Russia in support of Trump, what I don't get is this:  how can anyone possibly excuse the fact that Trump went on a narcissistic fantasy WITH ZERO EVIDENCE that Reiner was murdered because of his "Trump Derangement Syndrome".   I mean, it's an absolute invention (and an extremely unlikely one at that, given that the drug addled son was the suspect from the very start) that truly indicates a fabulist imagination so chronic that in many settings, you could see it cited as evidence for dementia and incapacity to make sound decisions.   

I mean, how are doctors going to reliably diagnose this man with dementia when he has invented bullshit, if not for his entire life, at least for the last couple of decades, and people just shrug and say "that's just Donald"?  

Given the attacks on Biden being tired and sometimes rambling, it just continues to be ridiculous that the media follows the MAGA line of "that's just Trump" when it comes to his continual lies and fabulist rhetoric.