This venue in Pittsburgh had two concerts, one of them one day and the other the day after. The first day was Kenny Chesney. The next, Marilyn Manson with Alice Cooper. As you can clearly see from the picture comparison, people who were at the Kenny Chesney show had no regard for their trash as they did for the metal concert.

Tailgating is something that people do at most concerts - especially Kenny Chesney. I think cleaning crews are used to having a couple of broken bottles, some litter and maybe even a few lost items. There's no way it could compare to how trashed the parking lot was after this country concert.

The parking lot at Marilyn Manson with Alice Cooper? After the late night cleaning crew took care of it, the parking lot looks nice and clean. According to the person who posted the pictures, "The smell of sun-roasted piss, stale bud light and chewing tobacco could be smelled blocks away. The lot needs power washed. The garbage on the river bank and floating in the river was bad enough to make a whole native American tribe shed a single tear."

To be fair, the metal concert picture was taken during the day, but there's no way it would ever be as trashed as what you see in the country concert photo.

Imgur

Update:
To further add to my theory, along came this news clip from the same show.