Obviously don't know what the agreement the nix has with the Stadium and Council but Gold Coast United put a cap of 5,000 supporters because that was a magic number, go over that and you have to hire more security, provide transport, etc. So it was cheaper to sell less than 5000 tickets than more.
It would go along way if we replaced the Yellow seats with something that is not so obviously empty. I always thought that if I ever bothered going to the Sevens again I would go as a yellow seat, just to fit in.