People keep claiming Martin is a slow writer. But I suspect he has books 6 & 7 mostly fleshed out and is instead capitalizing on the fame by pumping out other books as well as video games and such.

If one looks at his output bibliography, he is putting out material frequently. He published A Dance with Dragons in 2011-book five of seven in the series. He has since put out NINE more books with the most recent in 2022.

In addition to the last two books in the series, he has listed a sequel to Fire & Blood (about the rise of the Targeryans) and six other new books which are to be part of an entire new series!

https://en.wikipedia.org/wiki/George_R._R._Martin#Bibliography