Basically Rage was the Saturday headliner at PP4, but apparently not a lot of people wanted to see them. The result was about 400-500 people left in the venue when Rage came onstage. It was pretty unfortunate, considering the band put a really good show on.
I was under the impression the Rage effect also had something to do with Evergrey having an impromptu signing/meet and greet session after their set which caused most of the crowd to filter out so they could take advantage of that.