Despite The Winds of Winter taking so long, The Winds of Winter's release date delayed multiple times, to the point Martin no longer makes predictions about when it'll be finished.
Martin had originally hoped to finish both The Winds of Winter and its sequel, A Dream of Spring, before Game of Thrones finished its run. Of course, that didn't happen, and Game of Thrones season 8 delivered an ending before the books could, although one that is perhaps far more divisive than Martin's will be (or that's certainly the hope). The author has had no shortage of other projects in that time, developing Game of Thrones spinoffs like House of the Dragon, working on the Targaryen history book, Fire & Blood, upon which that show is based, and work outside of Westeros too, such as Elden Ring.
With the book so delayed, Martin has discussed intense demand for The Winds of Winter, saying: "I get [that] Winds of Winter, the sixth book is late. I can get a hundred good comments, but there's still gonna be a few fans out there who are gonna remind me of it on my blog or whatever," and mentioning that there can now be a "viciousness" in online discourse that wasn't there previously. Of course, anything that strays into harassment or abuse is completely unwarranted and should not be tolerated, but even among the much more good natured comments and demand for The Winds of Winter, there shouldn't be such concern. At this juncture, even with it taking so long, Martin has more than earned the right to patience, and to finishing the book on his when it's truly ready.
Why Is The Winds Of Winter Taking So Long?
It's true that it has been over a decade and counting without the release of a new The Winds of Winter's release delays don't feel quite so surprising or drastic.
That slower pace also speaks to the other issue, which is that the story is so much bigger now than when he was writing the first three books. A Dance With Dragons is more than 350 pages longer than A Game of Thrones, and even that is despite some events and characters being split across A Feast for Crows; The Winds of Winter will undoubtedly be longer still. The sheer scale of this story has kept expanding, with a dizzying number of plotlines and characters that Game of Thrones didn't even include; Martin has to reckon with servicing all of those, as well as begin to contract things again to set up the endgame and all of these things coalescing. That is one of the hardest tasks he'll have faced writing this series, especially as an author who typically doesn't map everything out in advance, but it's one he is surely up to given how great his story has been so far.
Martin has given promidates on The Winds of Winter and seems to be making decent pace, if not as much as an expectant audience or even himself would like in an ideal scenario, but too much demand and concerns about him not finishing or struggles to tell the story are unjustified. The author is telling the story his way, the same as it's always been, and the past justifies faith in him now. As far as A Song of Ice and Fire goes, Martin has not yet delivered a letdown in of story; The Winds of Winter is taking a long time, but there's also nothing so far to suggest it won't be worth the wait.