I feel like this is mostly cultural based on the event. Take two examples from my hometown. At Milwaukee Brewer's games thousands of folks drink and grill before the game, but most people clean up and it's not too bad afterwards. Across town at Summerfest they need earth movers and to remove the cups and cans.
Not so much Country vs. Other music, but peoples' expectations for the specific event determine the manners and hygeine. It sounds like the expectation for Country + Pittsburgh is to trash the place.