George R.R. Martin revealed that Game of Thrones wrapping after just eight seasons could not have been loyal to the source material.
Eight seasons of Game of Thrones ended up covering a lot of ground over the nearly decade-long run that it had. While characters received the various endings that they did, fans were not completely happy with where some of their favorites ended up. Divisive decision after divisive decision brought down the entire fandom in one fell swoop, destroying whatever faith that fans had built in creators David Benioff and D.B. Weiss.
George R.R. Martin believed that there were a lot of reasons why the show’s ending was not satisfactory. To begin with, the show was immensely different from the books, given that a number of characters were written out, and the remaining ones were killed. Some characters were added to the story, and hence, the makeup of it was completely changed. As far as the author of A Song of Ice and Fire is concerned, the show could have taken a little longer to end.
Game of Thrones could have gone on for five more seasons

One of the major criticisms of the later seasons of Game of Thrones was the fact that it felt like the world had been distilled or ‘dumbed down’, with a lot of its nuance lost. There was also the fact that it felt a little rushed, with characters killed off unsatisfyingly and receiving nonsensical endings (if they survived).
However, if the show were to be more accurate to the books, George R.R. Martin stated that at least five seasons would be required to do it justice, which would have caused Game of Thrones to have a total number of twelve seasons. Speaking to Fast Company magazine, he said (via Digital Spy):
The [final] series has been… not completely faithful. Otherwise, it would have to run another five seasons.
It is unlikely that there was any Thrones fan in the world who would have been against the idea of more Game of Thrones, as long as the characters and plots were better written and could recapture the quality and status of the first few seasons. However, that was likely not going to be the case. HBO does have a chance to fix its mistakes with the vast array of shows set in the world of Game of Thrones that it is developing, and here is hoping that they do not rush these as they did with Season 8.
A Knight of the Seven Kingdoms will be a different take on the world of A Song of Ice and Fire

A Knight of the Seven Kingdoms is going to be a whole different ball game than Game of Thrones or House of the Dragon. To begin with, this would be the first entry into the franchise that is going to entirely take place during peacetime in Westeros, and rather than following multiple characters is going to be focused on Duncan the Tall and his squire, Aegon the Fifth.
The story that will be in the series is going to be largely adapted from the Dunk and Egg short story series that Martin had penned, which has also proved to be widely popular with fans. While there are no great feuding families with big battle set pieces, the core idea of family drama is still going to be at the heart of the series.