Only because it was so bad
But that wasn't the claim made by the user I quoted. The claim was that it disappeared from everyone's minds, and yet here we are sharing links to articles where Charles Dance said he wasn't happy with the ending. It hasn't disappeared from everyone's minds at all. Fifteen months on and we're still having debates about it. Miriam Margoyles has been in the press this week talking about how she never watched the Harry Potter movies and only did it for the money. It's had basically zero coverage, except for Harry Potter subreddits and that, so does that mean Harry Potter's not culturally relevant? Of course not.
And that's without getting into the amount of complete idiots in American political commentary who've spent the week comparing Kamala Harris to Daenerys. And the amount of people who claimed 'Mad Woman' from Taylor Swift's new album was about Daenerys as well. The ending might have been shite for a lot of people but that doesn't mean it's been forgotten overnight like so many people continue to claim
over a year after it finished. It was one of the most-watched shows during lockdown and it recently won some poll on Digital Spy for the title of "Best TV show of the century". People who hated the ending still complain about it.
Now that Digital Spy poll is obviously complete bollocks because there's no way GoT is the best TV show of the last 20 years, but the evidence is there in black and white that people still talk about the show (
https://www.digitalspy.com/tv/a33467683/best-tv-shows-of-21st-century-revealed/). Hell, Charles Dance only passed comment on season 8 because an interviewer felt the need to ask him about it - because GoT gets clicks and traffic, because people are still interested in debating it regardless of whether they liked it or not. That the last season was good/bad/average is neither here nor there, people still talk about it.