there's no walking space behind stage, and the photographers would have annoyed more people if they cut through the crowd.
Photographers like them, are meant to be this way, if not, can you give them some of your best position to shoot a good pic? The photographers can't take their photographs without getting into good positions, and almost the entire stagefront was already taken up by the crowd, which meant that the stage was ironically the only place the photographers could photograph from.
the truth of the matter is, organizers have to hire photographers to photograph the event for the sponsors, more to show the turnout than the bands themselves. photos of the bands are important, sure, but are of little purpose to the sponsors. what the sponsors want to see is that their money went to good use and that there were many people there, and the stage is where photographers are best able to get shots that included both the bands and the crowd