I’d be really interested in reading a book or two covering the events immediately after the end of A Dance With Dragons, but alas, we probably never will.
My theory is that he was already well known but the show made him actually famous. He got caught up in celebrity life and his writing slowed down even more, and then, the shows ending really was his ending. And everyone thought it was fucking stupid. So he stopped writing. There will never be another main sequence book.
I'm less and less sure we'll get a satisfying conclusion to the events of the main series, but I've still got a lot of hope for Fire and Blood II and whatever continuation of the Dunk and Egg books we get. Summerhall and all that.