They're also at a point in terms of popularity where they're playing on smaller stages, who probably struggle to justify giving out 13 tickets for a 1 hour slot at 4am. I think it would be different if they were having to scrape together tickets to play on, say, the Other Stage (and essentially marketing the event via BBC highlights). The whole thing screams of him/them thinking they're a lot bigger than they are, and makes it embarrassing in future if they do want to play but have taken this stance. Play or don't play, but I don't think them not being there is going to significantly impact anyone's weekend (aside from their own).