Martin had years - literal years, over a decade - to finish the story how he intended.

The first three books in the series were published over the span of four years. If he had continued at that pace, the whole series would have been done well before the first season of the show dropped.

Even when the show first started in 2011, he could have finished the series well before the final season aired, and it could have been a more faithful adaptation of his intent.

He didn't. He has chosen to drag out the process. He has chosen to work on other projects, as is his right, but he had plenty of opportunities to get it done. He chose not to.