Y'know, for therapeutic reasons.
So, we've got Jabberwocky, obviously. Then you've got the Jim O'Rourke and Grizzly Bear ones that both got pushed back a few months and then cancelled altogether. Then there was the one MF Doom was meant to headline, which was a massive coup and the probable main reason a lot of people went, and they left it til the festival had begun to announce he wasn't gonna come. Admittedly that last one's small-fry compared to the others, but I was there so y'know.
What else? I know there are some big ones I'm missing...