Throw away consumerist society.
Anecdote from my little dear who was at Reading this year. (general festival age demographic: mainly late teens, apparently, or behaving as such)
(He did bring his tent back to sunny Suffolk, it was a pop up one he bought for the event, knowing about potential trashing. It had running water in every room ie single skinned with condensation. )
Discussion on the penultimate day in his group was along the lines of "everything gets trashed on the last night, shall we (not drink and) leave this evening? Conclusion was yes, apart from him and another couple who had pre-booked trains the next day.
That final night the little dear gets woken up by a disturbance so sticks his head out of popup. Nearby are a group of festivo yoof* pounding on a tent and flattening it. "what are you doing?" quoth he. "Don't worry, we aren't going to be doing your tent" they say, and continue. "But what are you doing though?", he persists, mindful of the fact that he might indeed become the next tent on the list, and drops out of site. Festivo yoofs get bored and depart under little dear's hidden watchful eyes. Person emerges from battered tent muttering "wtf?".
Little dear wonders why person didn't protest earlier; we shall never know.
Perhaps, in the same way as campsites have noise curfews which generally** work there ought to be a festival code of conduct which you specifically agree to buy buying your entry including no trashing of other people's stuff and taking your rubbish home with you including damaged items; also supplying a suitable no. of litter receptacles, assuming they don't already do so. Then asking festival goers to help with policing it. And make them feel bad when you randomly ask on the way out whether they've remembered to pack or bin everything.
*not his word and "yoof" on its own may have connotations
** don't always work, as I experienced this summer. Little dear took ear plugs.