You think The Kingkiller Chronicles will never be finished? I'd be quite disappointed by that.
His editor posted on social media that they haven't seen even a draft of the third book.
If you have hope that book 3 exists, I would caution you to reign in your expectations a bit.
The TV show started in 2011.
Kingkiller Chronicles is only 3 books, hardly epic. It's a trilogy. The first book came out in 2007, second in 2011, and nothing has been seen of the third, and presumably, final book.
Brandon Sanderson treats writing books as a job, thus he writes every day. Now you could argue that his books aren't as entertaining to you (subjective) or that his prose isn't as good (a bit less subjective), but he does treat his job like a job. Whereas Rothfuss and GRRM seem to try to do literally anything but continue writing their books.
Sanderson isn't a bot but he has something a lot of people lack, work ethic.
GRRM on the other hand agonizes over writing out perfect rough draft pages and thus never gets anything done.
Those that outline and plan ahead of time using the outline
Those that write the story as they write
Sanderson is very much an outliner, I think GRRM is more a it'll come together as I write it kind of person. He probably has some sort of plan, but it isn't as fine tuned as Sanderson's I suspect. Sanderson does multiple drafts as well, which works with how I write. My first draft may be complete trash, but getting it on paper helps me a lot in at least getting the ideas out and then I can fine tune or start over if I'm not happy at all.
But yes, I think Sanderson is very much a "I write regardless and I'll refine it over time" type of person and doesn't agonize over the little details until it's time to actually do that.