The only thing I can think of is the governing class was shocked and terrified by Trump winning the election and was scrambling for some kind of narrative, and so a random accusation used in the campaign became a Schelling point for "the resistance". It was not the result of cool deliberation, or thoughtful investigation into the facts. It was a cry of panic.
But once it became the thing people rallied around, the news couldn't just backtrack and say "Yeah, this is cringe. Please ignore."
So they had to keep pushing it, or at least pretend to treat it like it was a real story, and it was used as the cloak for impeachment and other types of political battles. This was the time when independent reporters like Glenn Greenwald and Matt Taibbi went full WTF mode on US news media, and were responsible for some of the most enjoyable picking apart of this narrative. Much better than the whole propaganda surrounding the invasion of Iraq, which was a war completely prosecuted on word-association - in which "Saddam" was pronounced next to "Al Qaeda" over and over again, in press conference after press conference and news reports ad nauseam until many otherwise honest people started saying "Yeah, they must be colluding together."
But that was nothing compared to hordes of angry New England soccer moms wearing pussy hats marching against KGB-puppets seizing control of their nation. Someone needs to make a movie.
But now there is no need for the "resistance" narrative and I'm sure almost everyone who participated in pushing that hoax turns a bit red when they look back on it. That's why you are not hearing a lot about it, just as people would prefer you not spend a lot of time thinking about Saddam's ties to Al Qaeda.