Wudang
BOFH
Honestly I think what happened is that writing novels is much harder than it looks, and Rothfuss lost control of his narrative somewhere in book 2. Neither he nor his editor could figure out how to get it back under control, and meanwhile he was diluting his focus and energy on a bunch of side projects. I think at some point he realized he just didn't have it in him to successfully wrangle all the potential and mystery boxes into a coherent and apt conclusion. So he's quietly given up.
I suspect so. I think he had a clear idea of the final book but even the clearest idea can be hard to commit to paper consistenly and coherently. He explained the 4 year gap between the first as being (partly?) due to writing a later part of the book then finding he had to the rewrite earlier parts. I suspect all the other activities are at least in part coping mechanisms to avoid facing book 3.
Shame, his Slow Regard of Silent Things was lovely.