Yes that's what I don't understand...going by previous years there'll be about five minutes between sets, so that's a hell of lot of people legging it from one stage to another. I understand it's the same every year (with second stage headliner finishing a few minutes before main stage headliner starts), but seems like a very similar demographic who would be there specifically to see both bands.
However, I'm no festival planning expert so I'm sure they know what they're doing.